https://gitlab.synchro.net/main/sbbs/-/issues/797#note_5861
You should have an auto-backup of your user.tab file in the data/user directory (e.g. user.0.tab) that you can restore, if you don't have another/more-recent backup.
As for the cause, it still sounds like a file system issue to me. One thing you can check/play-with is the SCFG->Nodes... "Keep Node File Open" option (which defaults to Yes), just in case there is a bug and interplay between an node.dab and the user.tab files (but I doubt it).
--- SBBSecho 3.21-Linux
* Origin: Vertrauen - [vert/cvs/bbs].synchro.net (1:103/705)