The SKSE function RegisterForMenu() needs to be refreshed on game load. In my recent mod released on nexus  it uses the function to track when the Book Menu is opened. It works great from initialization - however, after saving, exiting game and reloading game the function stopped working. It wasn't obvious why but I thought about it and simplified it down to just needing to be called in OnPlayerGameLoad() and that worked. The OnMenuOpen() events fired correctly. My point in telling you