Completlely uninstalling and reinstalling the game worked, and the save is saved even after a backup, but i don't understand how such files can just simply "disappear"

My dad was playing the game on a phsyical bought copy of the game (25th Anniversary version) and this one seems to use SCUMMVM However, my dad did a few progressions and saved, then left the game, but whenever he came in again a SCUMMVM message appeard with the following 8 important files are missin...