You have been right. Posteo verified that the error is caused by the broken event. After I have removed the event synchronization works now.
Thanks for your support!
On my Android 7 phone and using the latest DD 2.0 (gplay) release, I sometimes experience the following issue:
Hitting “Sync” in the calendar app responds quickly with “Calendars synced”, although I know that it did not correctly sync. Comparing with the calendar on my PC I know that the items have not actually been added/updated/removed.
Going to the DD app and syncing from there seems to fix it.
Currently not sure how to give more details. Does this sound like some known issue?
This is not a known problem. Syncing from various calendar apps works here.
Maybe it would help to know which calender app you’re using.