Guys I'm new to the forum as a writer.
I read threads here since 2013 and until this week all that I want was in one of those.
So let me explain the problem and what I've found and execute.
Device is a XT1033 running 5.0.2 OTA, no mods, bootlocker locked, not rooted, debug off, just an normal user. The device ran out of battery, and when boot up normally after the logo then the black screen (several threads about this), now and then the device boots normally but show an error called process.goggle.phone.com,.
Now what I've done tried to flash various 4.4.4 roms and higher, flash boot.img, flash recovery.img, custom recovery, adb sideload, wipe data, wipe cache, flashall, and nothing seems to even change whats in the emmc.
Currently I´m with unlock bootloader, I used device info and was able to retrieve some info these are in the first picture, I´m @ work right now, but if you guys need I can póst a log of device info.
My doubts are there is a way to enable debug mode from fastboot enviroment?
There is a way to root via some windows/linux tool?
When the device boots ot show mtp @ the windows but thats it, sometimes ot shows a !xt1033 in device manager.
I'll put some images here.
Can anyone help? I've read about blankflash, but not sure if it would work.
I was thinking about an otg solution via fastboot or something else.
Related
Hi,
After a serious software problems (crashed with 4.0.3 OTA update) i managed install a ROM, but my screentouch doesnt respond to my touch. The screen and all buttons function very well but i cant put the pin because touchscreen doenst work.
Could it be Software or is definitely Hardware?
Could be software. Have you tried flashing a new ROM (and appropriately wiping beforehand)?
Have you tried to access to the recovery ? Some recoveries use the touchscreen as the TWRP for example
Harbb said:
Could be software. Have you tried flashing a new ROM (and appropriately wiping beforehand)?
Click to expand...
Click to collapse
I try do clean install a custom rom and 2.3.6 OTA and in both the touch doesnt work.
I install the touch recovery, but after dont work i install a regular one via fastboot.
Clean install (format system, wipe everything, etc) and nothing work.
Will continue try another custom roms
Cyrille28410 said:
Have you tried to access to the recovery ? Some recoveries use the touchscreen as the TWRP for example
Click to expand...
Click to collapse
I can acess to recovery sometimes
When it fails push it in PC via fastboot.
Now i cant enter in recovery and cant connect via usb to flash another recovery
I'm screwed!
I cant get into recovery, when i pressed appears a android toy whith a warning sine.
I cant connect to PC, when in bootloader and connect to PC, in bottom appears "fastboot fails invalid command".
I´ve installed a stock rom 2.3.6 and the touch screen doesn´t work to iniciate the phone. Try to install franco kernell but it´s the same situation.
When i can connect the phone to PC i´ve try´de 3 different custom roms and none works.
Going to warranty.
Looks like your touchscreen may have just given up. Everything else is normal, you probably don't have fastboot/adb setup properly and that warning sign is the stock recovery. I'd sort out fastboot and lock the bootloader before sending it in. Also, if you don't have a backup of your sdcard you can mount it through a custom recovery (use "fastboot boot recovery.img").
Harbb said:
Looks like your touchscreen may have just given up. Everything else is normal, you probably don't have fastboot/adb setup properly and that warning sign is the stock recovery. I'd sort out fastboot and lock the bootloader before sending it in. Also, if you don't have a backup of your sdcard you can mount it through a custom recovery (use "fastboot boot recovery.img").
Click to expand...
Click to collapse
I´ve format SD card and have nothing inside.
"I'd sort out fastboot and lock the bootloader before sending it in"
How can i do that?
Remember that i cant access to recovery or turn on by computer.
Read the rooting guide or check out NexusSHacks.com, all the info you'll need.
How are you "pushing" recoverys via fastboot if you don't have fast boot set up properly?
Anyways. Speaking of fastboot. Get the official fastboot images for your phone and flash them all. If you still have issues with the screen its a hardware problem.
You should make a full backup and then flash the official factory images (ICS 4.0.4), made for your hardware version, through fastboot. You can find the exact version beneath your battery on a sticker.
If the problem persists after this, it's most likely a HW problem.
If the mobile is not recognized in bootloader / fastboot mode, then connect it to a Linux PC, and then post here the output of the following commands (as root):
Code:
tail /var/log/messages
Code:
lsusb
albundy2010 said:
How are you "pushing" recoverys via fastboot if you don't have fast boot set up properly?
Anyways. Speaking of fastboot. Get the official fastboot images for your phone and flash them all. If you still have issues with the screen its a hardware problem.
Click to expand...
Click to collapse
When i was able to connect the phone to pc i push it with code flashboot flash recovery Some.img
Now i cant "push it".
I cant enter in fastboot
I´ve been able to enter in recovery.
Unroot and back to stock.
Now already of screentoch doent work, some buttons dont work.
Going to warranty. Thanks everyone for the effort.
Hey all,
I have a big problem with my TF700.
I wanted to root my device after unlocking the bootloader through the app, but by being dumb I managed to delete the OS in TWRP (thought it was factory reset) and now I'm in big trouble.
The only thing the tablet loads now is the TWRP 2.2.1 recovery. (TWRP came with a root-package, I didn't install it myself.)
Since I can't load an OS that is apparently deleted, I'm stuck with using the (latest) SDK to get the stock rom back on the tablet.
The problem is, it doesn't work, at all. The device is recognised by my (Win7) PC and the 'adb devices' command gives me the ID and 'recovery'.
If I try to push the ROM to the Sdcard folder (or any folder, for that matter) It gives me a "protocol error" with no other explanation.
If I try to sideload it it is stuck on "Waiting for device".
I tried the 'shell' command, just to see what that does, but it also gives me an error.
Other commands can also give the the "error: closed" message.
Since both of those commands don't work, I can't get anything on this tablet, since I can't get this version of TWRP to mount an external (micro) SDcard, the option simply isn't there.
Can anyone help me with this, of has my tablet been reduced to an expensive paperweight?
That's the problem with packages - you don't really know what's in it...
What root package did you use?
You have a very outdated recovery installed. I'm guessing here, since you didn't post your bootloader version and that's the first thing we need to know!
Can you still get into the bootloader?
Boot with Power and Volume Down buttons until you see the tiny script and post your bootloader version. Should be something like 10.6.1.....
Do NOT do anything else in recovery at this point!!!! If it is incompatible with your bootloader you could hard brick!
Once we know if you have fastboot access and what your bootloader version is, we can help you to flash the correct recovery in fastboot. With that installed it's a piece of cake to get you up and running.
But be patient! Don't do anything else you're not quite sure of!
*Update Below*
I believe the culprit was the 'Install recovery' method "Scott's Recovery install tool"
I tried a few but most didn't do anything. Every tool I tried comes from the xda forums and checked youtube videos explaining the steps.
If I boot using Volume down + power, nothing extra happens. I just see in the left hand corner "this device is unlocked", since I unlocked the bootloader using the ASUS app.
If I use the command adb reboot bootloader, it goes to TWRP 2.2.1.
Does this imply that I also deleted the bootloader?
Update: I deleted all drivers and software regarding the tablet from my PC and I installed the adb setup package from these forums and reinstalled the (universal?) driver package. This turned out to be a newer version of adb, and I actually managed to push a file to the tablet with no problems. I am reluctant to try anything else at the moment, since this whole ordeal had given me quite the scare (and the desire to learn more about this all)
Can anyone help me revive my tablet?
FooYoungHi said:
*Update Below*
I believe the culprit was the 'Install recovery' method "Scott's Recovery install tool"
I tried a few but most didn't do anything. Every tool I tried comes from the xda forums and checked youtube videos explaining the steps.
If I boot using Volume down + power, nothing extra happens. I just see in the left hand corner "this device is unlocked", since I unlocked the bootloader using the ASUS app.
If I use the command adb reboot bootloader, it goes to TWRP 2.2.1.
Does this imply that I also deleted the bootloader?
Update: I deleted all drivers and software regarding the tablet from my PC and I installed the adb setup package from these forums and reinstalled the (universal?) driver package. This turned out to be a newer version of adb, and I actually managed to push a file to the tablet with no problems. I am reluctant to try anything else at the moment, since this whole ordeal had given me quite the scare (and the desire to learn more about this all)
Can anyone help me revive my tablet?
Click to expand...
Click to collapse
Ok, good - you got adb working. The adb command to boot into the bootloader is
Code:
adb reboot-bootloader
Note the hyphen
Also I wonder if you pushed Power and Volume Down long enough. You should feel the tablet vibrate twice, then see some tiny script and 3 icons appear. That would be the bootloader menu and in it, you are in fastboot mode by default.
The next step would be to check if you have a fastboot connection.
The command for that is
Code:
fastboot devices
Read my guide on flashing a custom recovery and rom very carefully and follow the steps outlined to get TWRP 2.8.0.1 on your tablet.
Ask any questions you may have in that thread.
http://forum.xda-developers.com/showthread.php?t=2688891
Edit: Sorry, forgot that we have to determine your bootloader version first. So use the button combination or the adb command to boot into it and post it. Don't worry. I don't think you did anything to the bootloader - it's not that easy to mess it up...
Unfortunately, the adb code doesn't work, with or without the hyphen. The device will reboot, but will return to TWRP.
I've held down the Volume down+power button for more than a minute witout result. The device will just reboot after a while for as long as I'm holding it. I do see the screen flicker for a second.
I've also noticed, that after I push a file to the tablet, that after a reboot it loses the data I just moved.
After booting TWRP, when I look in the command line of TWRP, it tells me that it can't mount the 'system' , 'data' and 'cache' forders. (tw_mount)
And it specifically mentions (multiple times) that the /data folder failed to mount, giving the message "No such file or directory"
It seems I really managed to F'ed it up good...
My "force-boot-to-bootloader" kernel module might help you unbrick. Read this guide very carefully before you do anything:
http://forum.xda-developers.com/transformer-tf700/help/guide-t2853546
You people are my new heroes!
The last guide did the trick. The stock firmware is installed and I'm currently updating and installing all the apps.
Thank you all só much, you really saved me a ton of frustration.
Hello Everyone. Normally I´m the quiet Reader and not the Active Poster but I need your help guys.
I have a problem since yesterday and I tried to fix it by myself with searching everywhere but couldn´t do it by myself.
What I had before:
Optipop 5.0.2 with Racer Kernel (both had Builds from January) + TWRP 2.8.1
What I wanted to do:
Flash Grogg's AOSP 5.1 and newest Code Blue Kernel
What happenend:
I factory resetted and successfully flashed Grogg's AOSP 5.1 and Code Blue Kernel but had Problems with FCing Clock and Dialer so I tried to reflash both after wiping completely (even internal storage), mounted it and put the needed new files on the internal storage.
I reflashed the Custom Rom + Custom Kernel and the newest Radio, wiped Cache/Dalvik and rebooted. It booted and the notification screen with 'optimizing apps' appeared. After that that screen went black and nothing else.
It was lit so I´knew that the device wasn´t shut down and tried to rebbot sincee nothing happened. I noticed that it was possible to reboot or shut down the device normally so there might have been a Problem with the Rom.
I retried the whole procedure and this time the notification screen didn´t show up after the boot logo and went directly to the black blank screen but i still had the possibility to rebbot/shut down the device normally. This time I didn´t wipe the whole storage and this time it got stuck at the boot logo and the Custom Recovery seems to be broken, too. The screen shows the dead Android with the red triangle.
My Problem is that I can´t connect my device to the computer, find it with 'adb devices' and reflash the Recovery with fastboot. The device is shown as 'android' in device manager in Windows 7 and nothing else. I already tried to un- and reinstall the Google drivers and that whole stuff but it doesn´t work for God's sake. adb doesn´t list my device and the 'list of devices attached' is blank although my device is connected.
I know my phone is soft bricked and that it is possible to fix that although I don´t know why it even broke the OS and Custom Recovery.
Can anyone help me out with a step-for-step-guide to fix the adb Problem and explain me why that blank screen even happenend?
Edit: If I´m in fastboot mode the device is shown as >Android Bootloader Interface< and isn´t listed with 'adb devices'. If it is powered off it is shown as >Android Composite ADB Interface< but is listed with 'adb devices' but I can´t flash the Custom Recovery.
Beyazid said:
My Problem is that I can´t connect my device to the adb to reflash the Recovery.
Click to expand...
Click to collapse
You don't use adb to flash a custom recovery. You use fastboot. That's your first problem.
I actually meant that it isn´t shown with the command 'adb devices' I will change that in the text
Edit: I also noticed that the fastboot mode is always on in the bootloader although the device isn´t connected to the pc. Shouldn´t it only be active if it´s connected?
Beyazid said:
I actually meant that it isn´t shown with the command 'adb devices' I will change that in the text
Edit: I also noticed that the fastboot mode is always on in the bootloader although the device isn´t connected to the pc. Shouldn´t it only be active if it´s connected?
Click to expand...
Click to collapse
I see a couple problems here.
First one is use the newest version of TWRP. You can get that from my signature.
Second is Code_Blue may not be compatible with the ROM you are testing.
You don't need ADB at all for this, you need fastboot.
As I said. I just use adb to make sure that my device is found by and connected to the pc. I know that fastboot is used to flash everything but my Nexus 5 isn´t even shown. So how can I get my phone connected to flash the custom recovery?
And it seems like it is compatible since it worked the after the first installation and boot
FFS, XDA. I had just written a huge ass post on how to use fastboot properly, with the proper commands and ****, and you logged me out, making me lose all that. F U.
Beyazid said:
and the Custom Recovery seems to be broken, too. The screen shows the dead Android with the red triangle.
Click to expand...
Click to collapse
This is the stock recovery.
You need to put your device in fastboot mode, REFLASH TWRP again with fastboot, then STRAIGHT FROM FASTBOOT select (with vol keys and Power) "Restart recovery". When you're in TWRP, wipe data/factory reset, reflash rom, gapps, REBOOT, PROFIT.
`fastboot devices` and `adb devices` are two commands to check if an active connection exists, between the host interface (on the PC, look at it as servers) and the device interface (look at it as clients). both commands will only return your device's SN IF drivers are correctly installed (speaking on a basic level, and about Windows). If you execute those commands, no SN comes up, then you need to fix drivers FIRST. Not even worth trying to do other commands.
`fastboot devices` only works here -> http://bazalabs.com/wp-content/uploads/2014/07/20140705_215603.jpg
`adb devices` works in TWRP/CWM (NOT in stock recovery) and in Android itself (needs USB Debugging active).
Thanks for the help. I was able to flash the Custom Recovery and the Custom Rom with and without Code Blue Kernel but in both ways the phone loads, sets up at the boot logo and goes straight into the blank black screen which appears without the notification screen of the apps that get optimized.
I can manually turn off, reboot.or take a screenshot which clearly indicates that the Rom itself is installed.
How can I fix that problem?
Thanks in advance
Edit: Tried with the Blue Code Kernel which gave that blank screen and wiped everything but internal storage and reflashed just the Custom Rom which gave me the same result
Could it be because the system.img or boot.img are missing??
Beyazid said:
Thanks for the help. I was able to flash the Custom Recovery and the Custom Rom with and without Code Blue Kernel but in both ways the phone loads, sets up at the boot logo and goes straight into the blank black screen which appears without the notification screen of the apps that get optimized.
I can manually turn off, reboot.or take a screenshot which clearly indicates that the Rom itself is installed.
How can I fix that problem?
Thanks in advance
Edit: Tried with the Blue Code Kernel which gave that blank screen and wiped everything but internal storage and reflashed just the Custom Rom which gave me the same result
Could it be because the system.img or boot.img are missing??
Click to expand...
Click to collapse
Try another ROM.
System.img .. boot.img.. comes with the ROM you flashed (well, not exactly, but both partitions do get written to), so no, they're not missing.
I gave it another try and fixed it.
I'll write it down so anybody who ever faces that problem can solve that, too.
Follow that guide (http://forum.xda-developers.com/google-nexus-5/general/tutorial-how-to-flash-factory-image-t2513701) step by step and after a few minutes of flashing and a few minutes of booting you should get a clean and fresh Android Version on your device. It removes all the old files and installs the newest files.
And thanks guys for helping me out with that adb/fastboot mistake. Kudos to you
Hi! I'm kind of new to this so please forgive me (done once before with a few problems).
Basically, I was looking to root my new HomTom HT16 with SuperSU by downloading a custom recovery (TWRP). I rebooted into bootloader with USB Debugging enabled and OEM Unlocking enabled too.
I selected Fastboot mode from the menu in the bootloader and plugged my phone into my computer. I had no problems recognising the device. I followed the bootloader unlocking steps with:
{fastboot oem unlock}
The instructions that I was originally followed told me that I had to use the Fastboot command (with the recovery.img being TWRP):
{fastboot flash recovery recovery.img}
I was told nowhere that I had to clear any cache partitions (still not sure if I had too). Everything I did seemed successful until I was told to take the battery out, put it back in and turn the device on. It brought up the "HOMTOM" text for the boot screen but instead of booting, it repeatedly turned off and on. Because none of this actually worked, it didn't actually flash the recovery, and so I couldn't boot to it. It just got stuck in a boot loop.
I searched up how to fix a bootloop and I could find anywhere a solid solution unless I just wasn't looking properly. I have all the factory ROM files, I just don't know how to use them to replace anything that could be corrupted. I flashed back the original recovery.img but it still will not turn on, it just says on the "HOMTOM" text screen for a very long time. The recovery also doesn't work, it's just an image of broken android with its internals showing.
Does anyone know what to do now?
adamshaw said:
Hi! I'm kind of new to this so please forgive me (done once before with a few problems).
Basically, I was looking to root my new HomTom HT16 with SuperSU by downloading a custom recovery (TWRP). I rebooted into bootloader with USB Debugging enabled and OEM Unlocking enabled too.
I selected Fastboot mode from the menu in the bootloader and plugged my phone into my computer. I had no problems recognising the device. I followed the bootloader unlocking steps with:
{fastboot oem unlock}
The instructions that I was originally followed told me that I had to use the Fastboot command (with the recovery.img being TWRP):
{fastboot flash recovery recovery.img}
I was told nowhere that I had to clear any cache partitions (still not sure if I had too). Everything I did seemed successful until I was told to take the battery out, put it back in and turn the device on. It brought up the "HOMTOM" text for the boot screen but instead of booting, it repeatedly turned off and on. Because none of this actually worked, it didn't actually flash the recovery, and so I couldn't boot to it. It just got stuck in a boot loop.
I searched up how to fix a bootloop and I could find anywhere a solid solution unless I just wasn't looking properly. I have all the factory ROM files, I just don't know how to use them to replace anything that could be corrupted. I flashed back the original recovery.img but it still will not turn on, it just says on the "HOMTOM" text screen for a very long time. The recovery also doesn't work, it's just an image of broken android with its internals showing.
Does anyone know what to do now?
Click to expand...
Click to collapse
Do you say you have the original files if yes, then if your device is a Mediatek device use SP Flash Tool to flash the rom. If you still need help contact me here or on [email protected]
I haven't really touched this tablet in a while, but i wanted to start using it again. I was running BlissPop. It was slow, and kept giving me an error when it was trying to update, so I decided to try a different ROM. So I downloaded the lineageOS ROM and tried to flash it.
However, TWRP kept giving me an error when I tried to flash the ROM. I don't remember exactly what the error was.
So, I thought that I needed to update TWRP. I tried through the "Official TWRP" app, but after doing so I was unable to boot into recovery mode at all. I could still get to the bootloader, but when I tried to select recovery mode it would give me an error and dump me back out to the bootloader menu.
I tried installing twrp through "TWRP Manager" app, but it just says "something went wrong"
I tried doing this using ADB. I connected the tablet, enabled USB debugging. If i do the ">adb devices" command, I can see the tablet. Then I did >adb reboot bootloader - which works, it reboots the device into the bootloader. But then I try and flash recovery and nothing happens, it just says <waiting for device>. And if I do > fastboot devices it doesn't list any devices.
If I reboot to the bootloader and select "Recovery Mode' i just get the nvidia boot logo and it stays there forever.
I don't know what else to try at this point.
I think I could get this to work if I could just get fastboot to recognize my device, but I'm not sure what's preventing that from happening.
mattlokk said:
I haven't really touched this tablet in a while, but i wanted to start using it again. I was running BlissPop. It was slow, and kept giving me an error when it was trying to update, so I decided to try a different ROM. So I downloaded the lineageOS ROM and tried to flash it.
However, TWRP kept giving me an error when I tried to flash the ROM. I don't remember exactly what the error was.
So, I thought that I needed to update TWRP. I tried through the "Official TWRP" app, but after doing so I was unable to boot into recovery mode at all. I could still get to the bootloader, but when I tried to select recovery mode it would give me an error and dump me back out to the bootloader menu.
I tried installing twrp through "TWRP Manager" app, but it just says "something went wrong"
I tried doing this using ADB. I connected the tablet, enabled USB debugging. If i do the ">adb devices" command, I can see the tablet. Then I did >adb reboot bootloader - which works, it reboots the device into the bootloader. But then I try and flash recovery and nothing happens, it just says <waiting for device>. And if I do > fastboot devices it doesn't list any devices.
If I reboot to the bootloader and select "Recovery Mode' i just get the nvidia boot logo and it stays there forever.
I don't know what else to try at this point.
I think I could get this to work if I could just get fastboot to recognize my device, but I'm not sure what's preventing that from happening.
Click to expand...
Click to collapse
Did you set:
Allow oem unlock in dev opt.
Fastboot protocol into BL?
Twrp app & manager need root to work.
Just flash the latest stock ROM first, lineageos requires having latest firmware.
I wrote a little guide not long ago about that (obviously, you can skip the F2FS steps if you don't need F2FS and just flash ROM after flashing latest TWRP)
Link
thanks for the help, i'll try and work through this soon.
fpozar said:
Just flash the latest stock ROM first, lineageos requires having latest firmware.
I wrote a little guide not long ago about that (obviously, you can skip the F2FS steps if you don't need F2FS and just flash ROM after flashing latest TWRP)
Link
Click to expand...
Click to collapse
I had seen your thread, and was intending on following it. nice post. 2 quick questions though
1) this is a shield tablet that was supposed to be remotely bricked by nvidia after the warranty claim. Will that happen if I flash the official recovery ROM?
2) how would I even flash that rom if I can't get recovery mode to work in trwp?
I think the root problem that I'm having is that I can't seem to connect to the device via fastboot (i'm sure i used the wrong terminology somehow)
edit: well I downloaded the USB driver for the shield tablet from nvidia, and i was able to install that (rather than the google usb driver). Fastboot finally recognized my device after that. I'm trying to flash the recovery now, but it doesn't seem to be doing anything, just been stuck on this screen for a while now: https://i.imgur.com/BUwj3Hx.png guess I'll continue to wait a while.
edit 2: well, finally got TWRP to flash over fastboot (https://i.imgur.com/tV1DqDv.png) however I still can't enter recovery mode. I just get the nvidia boot logo and then nothing happens. TWRP manager still says i don't have it installed either.
i'm about ready to give up on this... i've spent like 6 hours on this crap already and I feel like I keep getting further away from it.
mattlokk said:
I had seen your thread, and was intending on following it. nice post. 2 quick questions though
1) this is a shield tablet that was supposed to be remotely bricked by nvidia after the warranty claim. Will that happen if I flash the official recovery ROM?
2) how would I even flash that rom if I can't get recovery mode to work in trwp?
I think the root problem that I'm having is that I can't seem to connect to the device via fastboot (i'm sure i used the wrong terminology somehow)
edit: well I downloaded the USB driver for the shield tablet from nvidia, and i was able to install that (rather than the google usb driver). Fastboot finally recognized my device after that. I'm trying to flash the recovery now, but it doesn't seem to be doing anything, just been stuck on this screen for a while now: https://i.imgur.com/BUwj3Hx.png guess I'll continue to wait a while.
edit 2: well, finally got TWRP to flash over fastboot (https://i.imgur.com/tV1DqDv.png) however I still can't enter recovery mode. I just get the nvidia boot logo and then nothing happens. TWRP manager still says i don't have it installed either.
i'm about ready to give up on this... i've spent like 6 hours on this crap already and I feel like I keep getting further away from it.
Click to expand...
Click to collapse
Okay so I'm guessing you have stock ROM.
To flash TWRP you have to enter fastboot mode (vol down + power I believe) and flash the twrp image with fastboot flash recovery twrp.img (rename the shield tablet twrp to just twrp.img and place it into your easy adb and fastboot folder)
And DON'T reboot into OS, rather use your volume buttons to navigate to "restart to recovery" or just use hardware keys again directly from TWRP (vol up + power).
Good luck
fpozar said:
And DON'T reboot into OS, rather use your volume buttons to navigate to "restart to recovery" or just use hardware keys again directly from TWRP (vol up + power).
Good luck
Click to expand...
Click to collapse
Agreed. This is probably what is happening (as described on the TWRP webpage here:
Note many devices will replace your custom recovery automatically during first boot. To prevent this, use Google to find the proper key combo to enter recovery. After typing fastboot reboot, hold the key combo and boot to TWRP. Once TWRP is booted, TWRP will patch the stock ROM to prevent the stock ROM from replacing TWRP. If you don't follow this step, you will have to repeat the install.
Alternately, immediately rooting (flash SuperSU or Magisk) right after flashing TWRP, will prevent TWRP from being replaced with stock recovery.
Although the inconsistent fastboot connection, and how much trouble you had flashing TWRP initially, is a bit worrisome. Try using a different cable (maybe the one you are using is not connecting well?) try another USB port on the computer, and don't use a USB hub (connect direct to the PC).
Well, like they say: persistence is key. I kept pushing and trying new things until eventually.... I bricked the device. No, not really, it's working great now on LineageOS.
Thanks again to everyone who helped me out :good:. I'm still not sure exactly what caused TWRP to stop working on my device, however following this guide helped me fix it: https://forum.xda-developers.com/shield-tablet/help/help-stuck-nvidia-boot-screen-t3076462
The "flash-all.bat" restored everything to stock (including the recovery mode) and after that I was able to flash the latest TWRP and install Lineage.