It seems that in the past few days, something has happened that is causing several posts, in several threads, to be missing.
I have not yet analyzed anything about this. It would be interesting to know whether the posts are completely missing from the database, or if they exist but aren't being displayed.
I don't have time to investigate this now. I sincerely hope it's not a big issue because it would be a PAIN to fix. My hosting provider does make backups, even of the database, but restoring that would mean losing any new posts that were done in the meantime. Given enough time, one could probably do a clever merge of the backup into the current system, but that's something I don't dare touch.
If you have additional information / questions / suggestions, please don't hesitate to share them here!