A friend who logged in to the server, using the same PSN account and Microsoft account as always, has been treated as a new player by the game and has lost all his inventory and access to his Ender Chest inventory as well - as expected. Rolling back the save file has not worked, and he has attempted to log out and back in several times. Unfortunately, there is no "emergency cheat mode" that won't ruin trophies on the save file permanently, so without using a third-party application to edit the save file and re-associate his old inventory with what is probably a mistakenly assigned new player ID, I can't help him.