[Thinkpad Tablet Android Development] dave457:
OK. I had a slight issue with this ROM in so much that the compass sensor was not functioning correctly but this could be down to Lineage 17 (and 16). See "update" at the end.

Anyway, returning to stock Android 8.1.0 did not prove easy. I tried many suggested methods and many fake websites, but because it's quite old now most of the downloads had gone or simply didn't work anymore including the Lenovo Rescue etc.

I eventually found the required files, so if anyone wishes to go back to stock Android 8 on TB-8704F then I made a note of my steps and hosted the required files. Here's my quick "how to" and it may help others.

Lenovo Tab 4 8 Plus - TB-8704F Only - Return to stock Oreo 8.1.0

================================================================

Download img files from:

File on MEGA

mega.nz

or

Factory image LenovoTAB4_8Plus.zip

drive.google.com

1. Go into TWRP and do a backup of all Lineage 17.1 partitions

2. Factory reset

3. Wipe all partitions but NOT EFS, BOOT, Recovery or SD Card, i.e wipe System, Data, Cache etc

Unzip all three files from the zip and then boot tablet into Fastboot mode, then as 3 seperate commands:

fastboot flash boot boot.img

fastboot flash recovery recovery.img

fastboot flash system system.img

When flashing system you wil get the following message and it will pause/stop

"Invalid sparse file format at header magic"

I just pressed Ctrl-C (perhaps any key would have worked) and it carried on without errors

Sending sparse 'system' 1/7 (519763 KB) OKAY [ 11.894s]

Writing 'system' OKAY [ 14.856s]

Sending sparse 'system' 2/7 (521748 KB) OKAY [ 11.726s]

Writing 'system' OKAY [ 14.144s]

Sending sparse 'system' 3/7 (520839 KB) OKAY [ 11.715s]

Writing 'system' OKAY [ 14.055s]

Sending sparse 'system' 4/7 (485244 KB) OKAY [ 10.969s]

Writing 'system' OKAY [ 13.151s]

Sending sparse 'system' 5/7 (520428 KB) OKAY [ 11.771s]

Writing 'system' OKAY [ 24.616s]

Sending sparse 'system' 6/7 (517514 KB) OKAY [ 11.714s]

Writing 'system' OKAY [ 23.773s]

Sending sparse 'system' 7/7 (496445 KB) OKAY [ 11.285s]

Writing 'system' OKAY [ 20.179s]

Re-boot and stock Android 8.1.0 is back. Note: First boot can take a while. Patience.

Check for updates after setup. There are two later versions available via OTA

During the first OTA Update you will receive an error

"unknown flag verity" error at the end of the update

After the update boot into stock Recovery and Factory reset and wipe cache

Then reboot. It will encrypt the device and reboot

Go through Setup again

OTA update again. No errors this time.

You will finish up with TB-8704F_S001018_191009_ROW

Security patch: 5 August 2019

Hope that helps.

UPDATE

=======

Well it's been a while since I flashed ROMs on this device and I now remember this model of tablet does NOT have a compass sensor so nothing wrong with this ROM :)

But it does have GPS and for navigation I have tested Sygic, CoPilot, Nokia Here and Google Maps (all using offline maps) and they all work fine. In fact I have been using Sygic for a number of years on this device and it's much faster and better then my old Nexus 7 (2013). So using Linage or stock there is no compass because there is no sensor fitted :)

Anyway, the above procedure may still be useful for anyone wishing to return to stock Oreo.