This has been a bug for the last year. I’m not sure what causes it, but I recommend checking your event log. Do something that will cause it to update, such as picking up something from a chest or dropping an item and letting it decay. If it doesn’t update the event log, then it’s not going to save. Make sure the event log is updating to your last change before logging out. Also, quit to the main menu first, don’t just quit the game entirely.