Since I couldn't figure out what happened and how to repair the FFS directory structure, and re-transferred the #AmigaOS 3.2 system I normally use in UAE.
The problem never reappeared, so perhaps it was just FFS being prone to corruption when writes are interrupted by a crash. And this #Amiga was rebooted numerous times while I was chasing the remaining hardware and software stability issues.
Anyway, these are some of the joys and sorrows of #vintagecomputing ❤️