You got output from getvar current-slot as current slot:_a, is that correct? Not seen that before; would guess that’s not normal. I’m guessing you switched a rebooted to a all via fastboot. Maybe it just didn’t work properly and is still viable; but is it worth your time to investigate and have another go?
Back in Aug I did a clean install of pie testbuild 0.9 for pioneer. Bit later eOS asks people to do a clean install of pie test build 0.10 “improved version which would take ota’s”. I did this, but did not format data. Everything worked, I had my data and a few days later an ota arrived which again worked ok. So my dirty flashing didn’t seem to upset anything. I’ve been on the same build since then with no updates waiting patiently for something else to happen at e!
So maybe it is worth trying a dirty flash from slot b to end up with 0.11 on a, your call. I find it useful at all times on XA2 to manually reboot to recovery after sideloading the zip to check the slot and reboot system from there. Once or twice there has been a problem picked up by recovery and factory reset has been prompted, so it’s not without risk of losing data.