Since several DAVdroid versions after an update to the app syncronization to OwnCloud 8.x (production version setting) gives errors. The other way (OwnCloud calendar to DAVdroid seems to work). From other threads I read this could be fixed with an upgrade to oC 9, but it seems 9 is half a year or more away from becoming production.
The immediate workarround by DAVdroid seems to delete and resetup the calendar. But this seems not enough. Un- and reinstall of DAVdroid seems to help (until the next app update). Not sure how to handle this, maybe by blocking any DAVdroid app updates.
9.0.4 is stable and ready for production. With older versions like 8.2.x you won't get any support anymore if you're facing issues with CalDAV and CardDAV as both apps previously providing this functionality are unsupported and unmaintained.
Thx. I will consider this though I would have hoped to avoid changing the Update-Channel setting and/or the main oC version now, because AFAIK it is connected to several other useful settings and updates (SSL URL Update, CalDAV URL update, etc.) with underlying settings change on all connected Apps. I will check for DAVdroid forums on this issue and maybe test other Android Apps before oC upgrade.