I’ve spotted recently, notes being closed by ContributionReviewer (which looks like a bot run by Pascal Neis, as its description says), which notes have as text "#NothingToDoHere - Reason: The initial user account has been removed or no longer exists". An example is this. I would assume such text being in comment of another user’s note (which account would have been deleted), and not being the note itself.
I haven’t found anything anywhere about this automated procedure. I would ask Pascal on Twitter, but since he doesn’t seem that active (except recently due to the outage), so I figured I would ask here if anyone else knows.