I may have been stumbling over this with caldav calendars. I could not consistently reproduce this behavior so did not bother to file a bug. I created an event on the server, deleted it, then created another one. The second one did not appear until restart, this did not happen all the time. I do wonder if this was the cause?
Bug 1716680 Comment 5 Edit History
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I may have been stumbling over this with caldav calendars. I could not consistently reproduce this behavior so did not bother to file a bug. I created an event on the server, deleted it, then created another one. The second one did not appear until restart, this did not happen all the time. I do wonder if this was the cause? Maybe bug 1684359 too?