On March 1, 2025, I confirmed that this issue is still occurring. (Windows 11 OUTLOOK_Classic). My PC also experienced a situation where Application_StartUP() would not start at all, but after making Application_Startup() and Quit() public, it started working. Even after reverting to private, it still starts normally. It might have been repaired by making only Application_Quit() public as well. In fact, I had a similar issue with Windows 7 that I had been using for a long time, where StartUP() would not start, but after changing it to public, it definitely started working. Thank you. This is a translation from Google. (From Japan)