Damnit! Pebcak here, for some weird reason all calendars in “acalendar” were excluded from syncronisation. After I enabled them again, everything is fine again.
Sorry for the mess, and many thanks for your support!
Setting color of single events discarded after sync
With Business Calendar it is possible to assign colors to specific events independently from the overall calendar color. After DavDroid sync, the individual colors are discarded. I disabled also “Manage calendar colors”, but I don’t think this is related.
Is this a (intended) behavior on the DavDroid side? Or just an issue on the Business Calendar side?
Please follow up at Single-event colors are reset when syncing.