Unable to sync with remote ics-URL

When I create a new subscription to a calendar, all entries in the calendar are loaded correctly.
If an event changes in the remote calendar, the entry in the Calendar app will not be updated.
The ICS URL comes from an Exchange server.
ICSdroid updates the calendar successfully. Also, the online view of the ICS URL is successfully updated. Only the calendar app remains outdated.
If I create a new share on the Exchange, it will also be loaded once correctly Updates are not loaded.

The nextcloud log shows no error. All other local calenders work properly.

What am I doing wrong?