That could happen if the database got restored to an earlier "save point", as part of wringing out problems with the new app.
Hmm, I know some computers, laptops had that function of restoring it to an earlier date and time when problems arose. I'd forgot all about that. But if the system locked up or something akin to that, restoring it to an earlier time might have been the only solution or the easiest.
Still it's frustrating losing posts. I can live with it, I only lost one. So from now on out, if my post is longer than a few lines that my memory can remember, I'll save it to word just in case.