In the GNOME Clock/Calendar Pop-up, which is revealed when you click on the date and time on the top bar, and also shows notifications and weather, shows me duplicates of some, but not all events. However, when I open the GNOME Calendar app or Evolution, which show all the same calendars and events, I don’t see any duplicates.
It’s confusing. And, I’ve carefully checked all my calendars for duplicates. If the same event is on two different calendars, it shows up as a duplicate in all views, and I can delete one copy from one calendar, leaving the remaining one on the other calendar. But, these particular duplicated events don’t seem to be on two different calendars. I’ve thoroughly searched all my shown calendars and only found these particular events on one calendar, the calendar on which I expect them to be on.
When I disable the source calendar that these events should be on, the calendar I put them on, the duplicate of each event goes away. But, these previously duplicated events still show up in the clock/calendar pop-up while the calendar app doesn’t show them! Phantom calendar events.
Aha! I think they are reminders for the event that are set to occur 10 (or 5 or whatever) minutes before the event, and the event itself. Not for native .ics calendars, but for my calendar that I convert to .ics and sync with radicale2 server. Hmm, okay, I think I figured it out. Not sure how to fix it, but I don’t think it’s a problem with the GNOME apps.