Everything has worked fine for years but suddenly 1 event I deleted several weeks ago will not go away. Many times a day I get the message shown above. The event does not show up on the google calendar when I look there. If I press "discard my changes and reload" the message pops back up within half a second. When I press "delete anyway" the popup does go away - but only for several hours.
Mac - 10.13.3
Provider for Google Calendar 3.3