That sounds like you created a sync conflict. See this comment for how that happens and what to do about it.
While restoring from an automatic backup (or a server-side backup) to get back to where you were before is usually possible, it’s not a good idea for you here, because you’d have to redo all of those reviews. In your situation, fixing the scheduling like I described in that other thread is a better solution.
Yes, add-ons are often the cause of sync conflicts.