[OnePlus 6T  Questions & Answers] oneboredmf:
So i've exhausted almost every xda thread I can find, and finally decided to make a post myself. This is maybe the 6th or 7th time I've had to MSM tool my phone because I softbricked and could only access bootloader. I'm a newbie so you may need to go in detail in what I should do. All help is very appreciated.

I'm trying to flash a new ROM to my phone, the one in question is the latest nightly build of LineageOS: lineage-17.1-20200806-nightly-fajita-signed.zip, the ROM itself works fine, however, flashing TWRP after flashing this rom (even if I wipe dalvik/cache) I no longer am able to access wifi). I've flashed stock and started over about 5-6 times (from the very very beginning, including unlocking the bootloader) and I'll always end up with a wifi issue or a bootloop.

I've tried multiple different versions of twrp, including the unofficial 3.3.1-32 Q unofficial builds from this guide and both 3.4.0-0 and 3.4.0-1 from the official website, both leading me to the same results. (the unofficial build wouldn't decrypt, so I failed with that one).

I'll go through the steps I do in detail, and if anyone sees an issue with my process, please correct me.

1- enabled developer options

2- enabled usb debugging and oem unlocking in developer options

3- booted into bootloader with

adb reboot bootloader

4- checked to see if phone is connected and unlocked the bootloader with

fastboot oem unlock

5- set up my phone again, enabled dev options, and enabled usb debugging again.

6- booted into bootloader again

7- typed this into the terminal to temporarily boot TWRP

fastboot boot <recovery_twrp>.img

7.5- flash copy-partitions.zip from the LineageOS install guide

8- went to advanced>adb sideload>swiped then went on adb terminal to sideload TWRP installer

adb sideload <twrp-installer>.zip

9- went to menu>reboot>recovery

10- after rebooting went to wipe>factory reset slide>swiped slider

11- went back to menu>advanced>adb sideload>swiped then went on adb terminal to sideload (while checking wipe cache/dalvik)

adb sideload <lineageOS-rom-nightly>.zip

12- tapped reboot system

this is where things begin to go wrong:

- i notice that I can't boot into lineageOS, lineageOS claims android data is corrupted and needs to factory reset

- factory reset phone

- boots up fine, go through set up process (wifi works right now, only problem I notice is that within build settings, it shows a completely different phone number on my SIM card rather than the phone number I actually have, but it doesn't look broken or corrupted), enable usb debugging again, boot into bootloader

- type

fastboot boot <recovery-twrp>.img

- twrp loads up fine

- go to menu>advanced>adb sideload>swipe to begin sideload then type

adb sideload <twrp_installer>.zip

- reboot system

- boot process takes forever, (restarts 3-4 times) phone feels sluggish, and wifi will no longer work (data works fine)

- i give up and I MSM tool my phone.

I genuinely think this is because of TWRP, I read through a few xda threads claiming that the official 3.4.x builds had many issues, and therefore would reccomend using 3.3.x builds. I tried both from the official website and the unofficial TWRP by mauronofrio, where i get decryption problems on both of them. only 3.4.0-x TWRP builds would get me as far as flashing the rom. I've tried this process on both android 10.3.0 and 10.3.5

I genuinely would like some help. this phone is my daily driver and not being able to use TWRP (let alone properly flash a ROM) is a big problem that destroys what I loved about my phone in the first place. Thanks in advance.