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Wipe help and bootloader

I have unlocked my boot loader which doesn't allow you to use recovery mode. Is there a way to completely wipe the phone and undo the bootloader thing? What program can you use. Also, how can you hide the bootloader unlocked start up screen? Thanks

I want to be sure you have all your ideas straight. How comfortable are you with working from the bootloader or from recovery? What tools do you use? Can you access recovery by this method?: Hold "Power" and "Volume Down" for ten seconds and release. This takes you to the bootloader. Then press "Volume Down" once to select the recovery, then press "Volume Up" to activate that option. This should then boot into the recovery. If that is not what happens, let us know what happens instead.
I have unlocked my boot loader which doesn't allow you to use recovery mode.
Click to expand...
Click to collapse
There should be no problem using any of the various recovery modes with an unlocked bootloader. Stock, TWRP, and CWM should all work fine. Can you describe what you did, what happened, and what you expected to happen?
Is there a way to completely wipe the phone and undo the bootloader thing?
Click to expand...
Click to collapse
There are several things here. You can wipe the phone and return it to factory defaults by using "fastboot -w". This does not change your bootloader or recovery. You can re-lock you bootloader, but it will always register that the bootloader was once unlocked. There is no real benefit to relocking the bootloader so I won't put instructions here, but let me know if that's what you want to do. Finally, you can flash a new recovery image onto your device, which will wipe out whatever recovery image you had on there. The command looks like "fastboot flash recovery recovery.img".
Also, how can you hide the bootloader unlocked start up screen?
Click to expand...
Click to collapse
This is simple as flashing a new logo. The command is "fastboot flash logo logo.bin". This will overwrite the stock logo (which checks if the phone is unlocked) with a modified one which looks the same whether it is unlocked or not.
See here for details and downloads: http://forum.xda-developers.com/showthread.php?t=2548530

FaultyFirmware said:
There should be no problem using any of the various recovery modes with an unlocked bootloader. Stock, TWRP, and CWM should all work fine.
You can wipe the phone and return it to factory defaults by using "fastboot -w". Finally, you can flash a new recovery image onto your device, which will wipe out whatever recovery image you had on there. The command looks like "fastboot flash recovery recovery.img".
The command is "fastboot flash logo logo.bin". http://forum.xda-developers.com/showthread.php?t=2548530
Click to expand...
Click to collapse
I mean fastboot recovery thing if that's what you didnt think.
I can get into the recovery screen fine. Selecting recovery puts me into a no command screen and then just boots up as normally. I was expecting to get another menu with factory reset and cache reset, and factory just boots up normally. Is factory reset from the fastboot screen just the same as the reset in the settings menu? Is it that you cant use those settings with a unlocked bootloader.
Are TWRP and CWN both apps you get for/through rooting in which you can restore back up etc? I have heard about CWN but havent really used it.
Would doing "fastboot -w" just do the same as reset from settings menu? Also I'm not sure what you mean by flash a new recovery image?
Also, I dont understand how to remove the boot loader unlocked screen. You have to start a command prompt and type in that with your phone in fastboot mode?
Is recovery
Sorry for being such stupid noob pleb :good:

I think I understand the problem. The first screen you come to says "Fastboot flash mode" or something like that and has a boot mode selection menu with "Recovery" as one option. This screen is the bootloader. When you are in the bootloader, you use the fastboot command on the computer to do things to the phone.
When you select and activate the "Recovery" option, you get a screen that says "No Command". This is actually the stock recovery. TWRP is TeamWin Recovery Project and CWM is Clockwork Mod. They're both roughly the same in terms to capabilities. Both have far more features than the stock recovery. You can use adb to communicate with your phone in recovery mode.
Here is a program that will help you install the recovery. USB debugging should be turned on on your phone, and you should be booted into the system. Also be sure that the proper USB drivers are installed on your computer.
http://forum.xda-developers.com/showthread.php?t=2635706
Here is the latest version of TWRP. You should download this image and use the above application to flash it.
http://forum.xda-developers.com/showthread.php?t=2561757
As always, ready everything carefully.

Could you explain the remove bootloader screen or how to relock bootloader?
Which one would you recommend: TWRP or CWN? Thanks! :good:

Banana4Life said:
Could you explain the remove bootloader screen or how to relock bootloader?
Which one would you recommend: TWRP or CWN? Thanks! :good:
Click to expand...
Click to collapse
http://forum.xda-developers.com/showthread.php?t=2548530
Why you need relock bootloader ?
Use philz recovery based on last cwm. It's amazing.

Could you explain the remove bootloader screen or how to relock bootloader?
Click to expand...
Click to collapse
Here is a thread about removing the warning screen: http://forum.xda-developers.com/showthread.php?t=2548530
In summary, you can either download "logo.zip" and install it from recovery, or you can download "original_logo.zip", extract "logo.bin" and use "fastboot flash logo logo.bin" when you are booted into the bootloader. I am assuming you do not have a "Google Play Edition" or "GPE". If you do, there is a different logo for you in that thread.
The bootloader can be relocked, but it will not change the warning screen. Locking the bootloader will only make it so you cannot flash custom recoveries and such. Can you explain what you hope to achieve by relocking the phone? Again, it can be done, but I want to make sure it is really what you want.
Which one would you recommend: TWRP or CWN? Thanks!
Click to expand...
Click to collapse
You can't go wrong with either TWRP or PhilZ. PhilZ is based on CWM. It has added features and touch capabilities. Because a recovery is so easy to switch, if you make your best guess for which you will like more, and if you are not happy with it, you can switch. I like both, and most users will find all the features they need in either one.
TWRP looks like this: https://www.xda-developers.com/wp-content/uploads/2013/11/AgsV.png
It can be downloaded here: http://forum.xda-developers.com/showthread.php?t=2561757
PhilZ can be downloaded here: http://forum.xda-developers.com/showthread.php?t=2639583
Its features and screenshots are here: http://forum.xda-developers.com/showthread.php?t=2201860

Can't flash twrp need help!

Okay so I received my opo today and wanted to unlock and root etc.. I managed to install drivers and download a toolkit which managed to unlock my bootloader but wouldn't flash the recovery so I attempted it manually via fastboot and after flashing it would reboot to a back screen then vibrate and reboot to system.. Been doing that all night? Any ideas? many thanks in advance new to this phone

Exactly what recovery version are you trying to flash? What OS is on the phone? Get rid of the toolkit, they're nothing but trouble.

Twrp 2.8.1. And its running android 4.4.4 cyanogen mod.. I have mate haha. I take it fastboot and adb are installed correctly as it shows my opo after typing fastboot devices and it unlocked my boot loader soo I'm confused

daviss101 said:
Twrp 2.8.1. And its running android 4.4.4 cyanogen mod.. I have mate haha. I take it fastboot and adb are installed correctly as it shows my opo after typing fastboot devices and it unlocked my boot loader soo I'm confused
Click to expand...
Click to collapse
Try flashing the recovery again, followed by this command
Code:
fastboot erase cache
Then:
Code:
fastboot reboot
Then try booting into recovery.
PS. You've unchecked the "update CM recovery" option in Developer Options, right?

same problem for me. tried manually installing any custom recovery, tried two different toolkits. it flashes and reboots, but then you can never enter the recovery app. even attempting to put stock back fails. i attempted the format the cache and that didn't do a thing for me. basically had to enable cm recovery updates and reset to factory in the os. after that i was back to scratch at least.

I was able to figure it out. Appears the version of TWRP is quite particular for some reason. Once I tried the latest build from here dl dot twrp dot me/bacon/ the problem was solved. Thanks for the tip @snickler

GrizzlyD said:
I was able to figure it out. Appears the version of TWRP is quite particular for some reason. Once I tried the latest build from here dl dot twrp dot me/bacon/ the problem was solved. Thanks for the tip @snickler
Click to expand...
Click to collapse
No problemo. ^_^

Bootloader Flash from TWRP (anything flash?)?

I was trying to install a ROM and things got a bit messed up. I wiped system/cache/dalvik/data via TWRP. I then went to install the ROM but it failed due to only supporting hhz12h bootloader.
So now I'm kind of stuck. I can't update the bootloader because fastboot/ADB won't list the device in TWRP. Is there any way to launch an ADB server in TWRP so I can fastboot the bootloader? Doesn't look like there is.
If there's not:
Is there a TWRP zip-install hhz12h bootloader I can use? Looked around, couldn't find one.
If not I'll have to try and find/flash the original image..but fastboot is not going to happen so I have to find a zip installable one that'll work with hhz12d bootloader...which hopefully is around. Otherwise I could install literally anything just to get an ADB server so I can fastboot the hhz12h bootloader in there. Stupid problem to have right here, lol.
Any thoughts/help is appreciated. TIA.

Okay, so I got around the issue. I'm not sure if TWRP is supposed to be able to fastboot or ADB but mine would not, I was under the impression that I could fastboot or ADB in recovery. Maybe that was just a mistake on my part thinking that.
My workaround:
- Reboot into the bootloader (not TWRP recovery), 3 finger reset, power off, then power button + vol up + vol down until you get the OEM Android bootloader screen (unplug if plugged in, it didn't seem to want to go into bootloader when it was plugged in - maybe I just didn't wait long enough, but unplug if it doesn't want to go into the bootloader).
- From here I was able to fastboot, "fastboot devices" listed it
- I then flashed the bootloader: "fastboot flash bootloader bootloader-hammerhead-hhz12h.img" (may differ if you wan to flash different bootloader)
- I then rebooted into bootloader: "fastboot reboot-bootloader"
- I then flashed recovery: "fastboot flash recovery openrecovery-twrp-2.8.5.2-hammerhead.img" (may differ for different version of recovery)
- I then used vol up/vol down to select "reboot recovery", and hit the power button
- TWRP booted and from there, now that I have the hhz12h.img bootloader flashed I could install the ROM, so I wiped data/dalvik/cache/system again, installed the ROM, installed Gapps, and rebooted, good to go.

FYI ADB works into recovery mode (TWRP) and Android. Fastboot can only be used when you are in the bootloader.
You did the right thing except that it wasn't necessary to flash TWRP. Flashing a bootloader.img only erases the boot partition so the recovery isn't concerned.

Primokorn said:
FYI ADB works into recovery mode (TWRP) and Android. Fastboot can only be used when you are in the bootloader.
You did the right thing except that it wasn't necessary to flash TWRP. Flashing a bootloader.img only erases the boot partition so the recovery isn't concerned.
Click to expand...
Click to collapse
Got it. For whatever reason I could not get ADB to see the device while I was in TWRP. I tried the ADB sideload feature in 'advanced' but it just waited and waited and waited forever. I believe ADB is set up properly on my system because it works fine on ROM. Not sure what the deal is with that, but I don't have much reason to go into ADB in recovery anyway aside from this issue, so it's [hopefully] not a big deal.
As for flashing the recovery, yeah, bad habit I guess. On my old phone (Fascinate Galaxy S 1), if you had custom recovery and had to 3-finger reset to bootloader because your phone wouldn't turn on or was bootlooping or whatever the recovery was boned, had to re-odin flash it. So it's stuck in my memory now that if I had to 3 finger it I better flash recovery. I'll try to knock myself out of that habit .
Thanks!

Syndacate said:
Is there a TWRP zip-install hhz12h bootloader I can use?
Click to expand...
Click to collapse
This one works.
http://forum.xda-developers.com/showpost.php?p=60879785&postcount=1246
EDIT - Looks like the poster took it down. I'll upload and get back to you.
EDIT part deux - http://d-h.st/zEex (includes the last modem)

Also that's a really old version of twrp you flashed...
Sent from my Nexus 5 using Tapatalk

Wakamatsu said:
This one works.
http://forum.xda-developers.com/showpost.php?p=60879785&postcount=1246
EDIT - Looks like the poster took it down. I'll upload and get back to you.
EDIT part deux - http://d-h.st/zEex (includes the last modem)
Click to expand...
Click to collapse
Thanks, I'll snag that just in case I ever have a fastboot outage or I'm on a system w/o ADB/fastboot or something.
ldubs said:
Also that's a really old version of twrp you flashed...
Sent from my Nexus 5 using Tapatalk
Click to expand...
Click to collapse
Haha, I didn't even look at the dates, I just went to the "Tools/Utilities" page for the Nexus 5 and it was the top link....I didn't think too much on it, just figured top link = most recent = latest.
http://forum.xda-developers.com/showthread.php?t=2511507
I'll dig around for a thread which has latest and flash that on there, can't expect old versions to work flawlessly, now can we?
EDIT:
That actually might have just been a copy/paste error on my part, as I had the old TWRP lying around for fastboot and copy/pasted the name from that. I used TWRP (ROOT) app to install and I chose latest (or so I thought). Now I have literally NO idea which one I was using -_-.

No worries glad you got it sorted. You can flash an image file in twrp now BTW.
Sent from my Nexus 5 using Tapatalk

Unbrickable tf300t

Hello everyone. I am new around here and totally new with android devices. I got my tf300t, installed twrp and flashed to the newest android version. Then my dad suddendly pressed something like restore to the manufactory setting and after that it rebooted and just keep booting with teamwin logo. I can not access twrp recovery mod, it is just in boot loop. I managed to get adb to work, but no fastboot since it does not boot into recovery mode. When I am in adb I can browse the device but the adb reboot bootloader does not work at all. It just hangs there. I can not power off the device because it does not let me, I can not boot into recovery mode with powerbutton and volume down button. After a long power button press it only reboots. I even tried with hard reset button but still the same. Could You please help me somehow? I really need that device for school and I would like to get back into the stock android. Thank you so much for any help.
//edit : I also forget to mention, when I execute adb deviced it shows:
List of devices attached
0123456789ABCDEF recovery
Also the device is unlocked.

Did you tried: adb reboot recovery ?
Did you tried to flash recovery again?
Be sure to use the right recovery for your bootloader. Did you upgraded bootloader to latest ASUS one? One then you're able to flash current recoveries like TWRP like 2.8.5.0 oder 2.8.7.0.
Edit: Also take a look here -> http://droidmodderx.com/prime/?page_id=74

Hello sir. Thank you for answering. I tried adb reboot recovery and it just hangs to be executed... But the tablet is still flashing the teamwin logo. I have the same bootloop as the guy on youtube called Francis Domingo and video called Samsung s5 stuck at TWRP Recovery boot loop (unfortunately I can not add link here).
//edit: Thank you for the link. It look like I have to use option 1a. Is it safe to use that command and I will not make it even more bricked? Thank you so much
//edit2: Now I just realized how to turn off the device to stop from rebooting. I just long pressed power button and up volume button and after the screen went black I kept holding the up volume button. I didn't work with down volume button or if I stopped holding the up volume button after black screen it rebooted again.
//edit3 : Let's say if I get to the twrp mode with option 1a from the link, what do I have to do next to get back to the stock rom (I think it was something like 4.0.3) ? Thank you

What the guy does in 1a is wiping mmcblk0p3.
Afaik mmcblk0p3 is the staging partition. That would be my guess anyway if you had access to fastboot. Usally when you can't boot into recovery, something is wrong in staging. I got the same problem 2 days ago. In this case you usually wipe staging partition via fastboot.
Since you got no fastboot access, you have to try with adb.
After cleaning the staging partition you can flash any recovery you want back again.
The recovery must be flashed to mmcblk0p4 <- 4!!! is the recovery partition. (but you should wipe mmcblk0p3 (3!!!) before)
So I would say, try what solution 1a suggests.
Edit: You can go back to stock android if you want, but there is no reason for this. My advice would be to unlock and root your device, upgrade to latest boot loader (which is done by upgrading to latest stock rom), then flash TWRP 2.8.5.0 and then a useful ROM on top. I'm using the one from timduru which is very nice. You can find it here: http://forum.xda-developers.com/transformer-tf300t/development/rom-t2932783

Thank you for the answer. Could you please write a step by step to get out of brick and to get the stock version, because the newer one I installed was many times slower. The reason why I would like to have step by step is because I don't wanna mess it even more than it is. Thank you so much.
//the stock rom was much more faster than the one I have installed, I mean... the boot time wad unbelievable slow, same with responses and wifi problem. If there is any other faster rom than stock I would be happy but I don't wanna mess with any bugs or slow boot speed and I can not wait minutes until it boots.

Hm, try the Option 1a from the link.
If done, boot into current recovery. Tell me which version and which recovery do you have.
Top on this we can decide what to do to flash a good ROM.

I had the exact same thing happen to me yesterday. Option #1 worked for me.
I did the steps from option #1 and powered down using the volume up + power. I then tried to boot into TWRP recovery, which only reproduced the same issue.
I redid the option #1 steps, and this time powered down using the power + volume down. I powered back up normally, and it rebooted normally into the ROM.
The tablet now works normally, and I can also boot back into TWRP recovery with no issues.
Thanks for the thread and the link.

Thank you so much Catscratch! After I executed both command from option 1a I can get into the screen, where it shows three options: RCK, Android, Wipe Data
In the top left corner, there is written:
Key driver not found.. Booting OS
Android cardhu-user bootloader <1.00 e> released by "WW_epad-10.6.1.27.5-20130902" A03
Starting Fastboot USB download protocol
The tablet can boot into the last ROM but as I said, I would like to have the faster and less buggy rom than this. When I open the settings and click about button there is written: CyanongenMod: 12.1-20150814-NIGHTLY-tf300t and Android version 5.1.1.
If I start RCK it just brings me back to the loop, but now I have fastboot available as it said above and I can list the fastboot devices on computer, which I couldn't before. Should I just execute this command from the computer "fastboot -i 0x0B05 flash system blob" and then "fastboot reboot" or should I download ROM from asus.com/Tablets/ASUS_Transformer_Pad_TF300T/HelpDesk_Download/ -> OS Android -> Firmware and now I don't know which should I choose: If JP or CN or WW or US or TW (Probably US right?). After that should I execute "fastboot -i 0x0B05 flash recovery firmware.img" and then "fastboot reboot" ? Or which ROM should I download to make it even faster and less buggy than stock ROM? Thank you so much again, You saved my tablet
//After I unzipped downloaded US ROM there is no img file. If I remember right the img file is only recovery to reflash the actual one and then when I start the twrp recovery I will select zip file with rom right?

OK, first of all to continue...I assume you got root access. (I think you should have, because you already got CM installed)
Next. Downloads.
Download: https://twrp.me/devices/asusTF300T.html
Also Download ROM+SuperSU: http://forum.xda-developers.com/transformer-tf300t/development/rom-t2932783
And GApps: http://forum.xda-developers.com/android/software/app-minimal-gapps-gapps-lp-20150107-1-t2997368
Push all files to sdcard with "adp push" or in CM. Like you want.
Flash TWRP. (you can skip this step if you already got TWRP 2.8.5.0 or higher version). You don't need latest one.
fastboot -i 0x0b05 flash recovery twrp.img
fastboot reboot
- or -
adb reboot recovery
Now, go into recovery and wipe everything:
- cache
- dalvik
- system
- data
After that flash ZIPs from sdcard. (use "add more zips" option)
1. ROM
2. Gapps
3. SuperSU
Next: Wipe cache and dalvik again (only these two).
Reboot and wait. First boot can take some minutes.

Thank you so much again. Everything work perfectly The rom looks a lot faster than the older one I had there. No issues yet at all. Just awesome. Thank you so much. Really appreciate your kindness and help. You have a nice day !

Thanks. Have fun with your tf300.

I somehow broke TWRP

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.