Nextcloud Android App: Calendar Backup only works for one calendar

Dear all,
I use a couple of calendars and I enabled daily backups in the Nextcloud Android App for contacts and calendars. Now I have noticed, that the backup only works for one of the calendars, ignoring all the others. May I have to add the calendars to the backup somehow/somewhere? Or might this be a known bug?

I’m running Nextcloud Hub 8 (29.0.7) on a virtual server. The Nextcloud App is from F-Droid store and version 3.30.0. But the problem must have existed for months if not years.

Maybe someone has an idea how I can debug this further?

Thanks a lot
Martin

not sure if this helps, but if you’re using DavX5 together with the Nextcloud app on Android for synchronising, all synchronised calendars seem to be backed up.

I’m not sure if I understand what you mean. I do use DavX5 and they get synchronized. But the backup does only create an .ics file for one calendar. My other calendars (including my “default” one for most of the appointments) are being ignored.