Comment # 8 on bug 1187392 from Reinhard Max

I am not sure I can follow you here.

If the machine crashed due to a power outage in November 2020 the FS corruption
should have been detected at the first boot after that rather than half a year
later.

Those fsck messages appear to come from booting into 15.3 for the first time
after the upgrade. Could it be that shutdown got stuck after the upgrade
(assuming it was done from the running system) and the machine had to be reset,
potentially leading to the FS corruption?