-48°C - ouch!!
I haven't heard of starting ether damaging O2 sensors - couldn't find any mention of that in a quick internet search. I would think if it could damage them, we'd see warnings on the cans and elsewhere, and/or you'd see "sensor safe" alternates to ether on the shelves. (I've seen discussions in which carburetor cleaner was recommended as an alternate to ether as a starting fluid, but that was due to the potential for engine damage due to severe pre-ignition from ether, no mention of sensor damage in such discussions. You'd think if it also damaged O2 sensors, those discussions would have been the perfect place tor warnings also of sensor damage - but have seen no such mention.)
"bank 2 left and right" - strange wording. To me, bank 2 means driver's side (left) bank.
Is that description from a scan code number? If you reset the codes, does that one come back?