KOrganizer <-> Nextcloud

Hi *,

does anyone else besides me have problems syncing calendars between KOrganizer 
(version 22.04.2-1.2 on openSUSE Tumbleweed) and Nextcloud (24.x)?
Synchronisation works for most of my calendar items, but not for all.

What doesn't work is
deleting an occurrence of a recurring event in KOrganizer isn't reflected in 
Nextcloud
deleting not recurring events sometimes isn't reflected in Nextcloud
modifying invitations (especially the invitation date) isn't reflected in 
Nextcloud

There are no error entries in the Nexcloud logs, but sometimes I get error 
messages in the client's journal like this one:

parse error from icalcomponent_new_from_string. string= "<?xml version=\"1.0\" 
encoding=\"utf-8\"?>\n<d:error xmlns:d=\"DAV:\" xmlns:s=\"http://sabredav.org/
ns\">\n  <s:exception>Sabre\\DAV\\Exception\\NotFound</s:exception>\n  
<s:message>Calendar object not found</s:message>\n</d:error>\n"

Any idea, whats going on here?
Why can the element not be found, though I can see it in my Nextcloud 
calendar, when opening it via Web interface?

TIA.

Bye.
Michael.