do you familiar with QFiL, i think you can try to clone the partition from your working tablet L1 (the brother) and apply on your current tablet. i mean whole partition.I've locked my device 3 months ago, it worked fine, I had Widevine L1 and everything , until I noticed 3 days ago that my widevine certificate downgraded to L3 even though the device is locked + the ''OEM CRYPTO API Version" downgraded too to v15 instead of v16. I was on .560 .
Naturally I thought that upgrading to ZUI 14 would fix this issue .. But it did not ..
So, I unlocked the bootloader, downgraded to 12.6.211 rechecked ''OEM CRYPTO API Version" and, reupgraded to v16 ! I did all the updates up to .560 ! At each update, I rechecked the version, and it remained v16. Until I updated to ZUI 14 through OTA with a chinese VPN and then the ''OEM CRYPTO API Version" changed back to v15. I tried relocking the bootloader, but it remained not only in v15, but I was still stuck with Widevine L3 ... This is such a weird, frustrating and disappointing issue from Lenovo ...
The problem is that after I upgraded to ZUI 14 ... I'm not able to lock the bootloader when I'm on .560 as it
Note that my brother (with the exact same tablet on .560) did not lose hist widevine L1 certificate.
Any help would be really appreciated