Time and date in calender web view uses wrong locale

Nextcloud 21.0.4, Language & Locale: German

The time in the display of calendar events in the browser uses the AM/PM format:

When opening the event also the date is not in the german format:

After deleting two shared calenders the display was correct again.
It seems, that sharing calendars from a user with different language settings (not locale!) started the problem.

did you find any solution