[OnePlus 7T ROMs, Kernels, Recoveries, & Other Deve] Nick-Henkey:
For anyone new, be sure to back up persist.img. After the last update my IMEI got deleted and it does not appear to be recoverable.

The update worked for about 1 week, it's possible my device just wasn't checked by the network for that week. It's also possible that T-Mobile deleted it since they just released a terms update today that says:

Just be aware and be careful! Loved this ROM while it lasted but water under the bridge now. Edit: "Love this ROM!"

Update 3/6/2021 - Phone fixed:

My phone is fixed. I did not update OOS before flashing AOSiP so this issue was very likely my fault. I had to

flash back to OOS and then re-flash AOSiP

. Full scenario and instructions are below; feel free to disregard the rest if you followed anirudhgupta109's instructions correctly.

Scenario

About 7 days after the February update the device no longer recognized the SIM card. When I attempted to re-flash OOS, the bootloader got half-way locked (showed as unlocked but would not let me do anything).

This was a factory and carrier unlocked phone, which was weird. As stated above, T-Mobile might have some super secret controls over our devices. The phone ran fine for 7 days after the February 13th update, so I did not think that it was caused by my inability to follow instructions. Still not 100% sure.

How it was fixed:

Gather latest images for flashing:

Download necessary files from this and the latest OOS from maronofrio's thread

anirudhgupta109 - https://aosip.dev/hotdogb

maronofrio - https://xdaforums.com/t/rom-stock-fastboot-op7t-stock-fastboot-roms-for-oneplus-7t.3979213/

Get Unlock code from T-Mobile

Gather info from command - `fastboot oem get_unlock_code`

Returned a blank IMEI for me, don't freak out

Locate your box or type in #06# to return your device IMEI

The unlock code should be clearly marked

Go to website and fill in the form - http://www.oneplus.com/unlock_token

Wait a week, and follow the instructions that get emailed to you....

Now you can flash OxygenOS

## Back up your data, this process will delete it ##

You now have to re-lock and re-unlock your bootloader. These were the commands I used in Manjaro (Arch) Linux

fastboot oem lock

sudo fastboot flash cust-unlock '/home/nick/Downloads/unlock_code.bin'

sudo fastboot oem unlock

sudo fastboot reboot bootloader

cd Downloads/OB1-GLOBAL-OnePlus7TOxygen_13.W.01_OTA_001_all_2003061944_9cb2036f4e514fe9-FASTBOOT

fastboot -w

Follow OOS re-flashing instructions here - https://xdaforums.com/t/rom-stock-fastboot-op7t-stock-fastboot-roms-for-oneplus-7t.3979213/

Now run all phone updates, this will take a bit, so grab a beer or 3

Re-Install AOSiP

Follow the instructions anirudhgupta109 posted at the beginning of this thread

Closing

When I saw that there was no IMEI I was worried that my persist.img file was corrupted, this happens sometimes with Samsung and OnePlus devices. To alleviate this concern for the future, I rooted the device (posted by anirudhgupta109) at the beginning of this thread. Once rooted, I was able to install a terminal emulator to back up recovery_a, recovery_b, and persist using the following instructions:

You will need to log into terminal as su

https://xdaforums.com/t/extracting-stock-boot-recovery-and-persist-images.4058447/