The issue resolved itself for me "magically" at some later time, either a Thunderbird update or more likely a Ubuntu update. Don't know what fixed it but it was so long ago that I had forgotten about it.
Thanks. I tried this without success.Your issue was related to a .ics calendar. I my scenario it is a "cloud based" CalDAV calendar and this might make the difference why unfortunately it is still not working here (Thunderbird by now on version 102.7...
Sticking to the original topic "Reminder-Window does not close after all reminders have been dismissed or snoozed" I experienced this issue starting with TB version 102.4.x as far as I remember. This continued through to version 102.4.2. I was excite...
