Well, I've tried it now, flashed the vendor.img to both slots, but it doesn't work. After flashimg the phone just allways reboots to fastboot mode. So, I did the full stock restore and it's now working again with the display touchscreen driver updated (or at least the touchscreen doesn't have the weird margin as before). So now I'm going back to Lineage. I was ready to do the full reflash anyway, so it's not a big deal the vendor.img reflash didn't work for me, but I wanted to give it a try at least.