Mac Calendar does not change appointments

I have a strange behaviour. I use caldav to sync my appointments from nextcloud to my mac calendar. There I can add a new appontment, but after that I cannot change it anymore. Not even delete it. Perhaps I drag the appointment to another day or time and after a few seconds it jumps back to the original place. Also when I delete it. It reappear within a few seconds.

I also use an android phone with DAVx2. And there everything works fine. I can move or delete a record and it stays as it is.

Has anybody an idea, what I can do?


Just some more infos … when I create the appointment in the nextcloud, I can move or delete it even on my mac calendar. Only when I create it on my mac, this strange behavior is there.

btw … with BusyCal everything works fine … so it has to be an issue with the mac calendar.