Thanks for the logs. DAVdroid adds the local calendars to the calendar storage:
09-04 23:16:42.242 16878 17091 I davdroid: [syncadapter.CalendarsSyncAdapterService] Adding local calendar
09-04 23:16:42.242 16878 17091 I davdroid: PARAMETER #0 = CollectionInfo(url=https://cloud.disroot.org/remote.php/dav/calendars/botbob/175e9fd0-2220-4b32-aab1-1c22e1c59997/, id=5, serviceID=2, type=CALENDAR, readOnly=false, forceReadOnly=false, displayName=vghj, description=null, color=-37632, timeZone=null, supportsVEVENT=true, supportsVTODO=true, selected=true, source=null, confirmed=false)
09-04 23:16:42.245 16878 17091 I ical4android: [AndroidCalendar] Creating local calendar: calendar_color=-37632 sync_events=1 canOrganizerRespond=1 ownerAccount=botbob@disroot.org visible=1 canModifyTimeZone=1 account_type=bitfire.at.davdroid allowedAttendeeTypes=0,2,1,3 allowedAvailability=0,1,2 name=https://cloud.disroot.org/remote.php/dav/calendars/botbob/175e9fd0-2220-4b32-aab1-1c22e1c59997/ allowedReminders=1,2 account_name=botbob@disroot.org calendar_access_level=700 calendar_displayName=vghj
...
apparently without errors. Later, the calendars are gone, because there are no calendars to sync before DAVdroid finishes.
I have seen this behavior with some sandbox and privacy guard features. I’m 90% sure that this is some kind of privacy guard problem.