Diagnostics for recurring appointments

I'm using OneCalendar to view some Nextcloud calendars that make use of weekly recurring events, including exceptions to those recurrences etc.

I'm seeing some "wrong" appointments in OneCalendar that I don't see in Nextcloud. Of course it is possible this is a Nextcloud problem and not a OneCalendar problem. To diagnose that, it might be possible if you can see some 'diagnostic' information about events, such as whether it is and 'exception' to a recurrence or a 'regular' recurrence, and perhaps the id of the (recurring) event?