Did you try to find a stock boot.img for the system.img you where flashing and then flash that to both slots? (BTW, which file did you take the imgs from?)I tried to install the things in this post, but I'm not on Windows, so I flashed the images manually. It didn't work.
I think there's something in the protected partitions preventing TWRP from booting, I have no idea. But that's where I am at, either trying to write to those protected partitions or finding a 'fastboot update' compatible archive, or getting TWRP to somehow work
It's so annoying that on these new AB phones you don't have the recovery partition. I think that if I could get TWRP somehow onto the device it might work. But it doesn't work with 'fastboot boot', it gives the qualcomm crashdump
You won't have TWRP on A11, but at least the phone should boot.
TWRP doesn't work for me flashed through fastboot. And I haven't tried anything else (like FKM I mentioned before). I am on stock 22.214.171.124 and rooted, don't need anything more than that.
And if that doesn't work, try to go back to A10.