Hi there,
since 1,5 years we use SOGo Server / Mailcow and emClient (Version: 8.2.1473 (04b618f)) with IMAP, CardDAV and CalDAV (automatic configured) and so far everything has always worked.
For about 2-3 weeks, subscribed (shared) calendars and own calendars have suddenly been ticked off / disappear for a short time completely from the overview and a few minutes later the reminders of old appointment entries appear and you can select the calendars again.
Even if you switch to the calendar tab, 95% of the time all calendars are deselected and you have to select them again. 5 minutes later everything is deselected again …
When the calendar is displayed, new entries can be made as well as deleted.
Thanks so much & best regards.