Tried stable, rc, devel... yep, and same result.
Just flashed Android rom, went perfectly fine, just like with OTA-15.
Isn't there any way to install UBports with sp_flashtool ?
For now I'll just keep it with Android. It's a bit sad, I mean, I bought the UT version for a reason when BQ started selling them... I didn't even really needed a tablet tbh.
I guess I should just buy a PinePhone!
Thanks hankschwie, Lakotaubp and everyone for all the replies and the time. If anyone comes up with a brilliant idea, I'm still interested though...