There seems something wrong with the contacts app then.
Please the nextcloud.log from the server then and details about your setup, like web server used, NC version and so on.
nextcloud.log is fine.
I checked the error message from dav on the droid:
it says:
…
<d:error xmlns:d=“DAV:” xmlns:s=“http://sabredav.org/ns”>
<s:exception>Sabre\DAV\Exception\NotFound</s:exception>
<s:message>Node with name ‘personal’ could not be found</s:message>
…
so it has nothing to do with contacts, but with the calendar.I disabled the calendar sync and will see whether the error comes again.
The Calendar app is providing two types of URLs; one for general applications (like DAVx5) and one for iOS/ macOS. I suggest trying the first one for general caldav applications.
in DAV I set all syncing to only manual, AND unchecked the checkboxes for syncing calendar and contacts. But I still get 404 error messages that an Addressbook with the name contacts can not be found.
why are my setting ignored, and why is the server still connected for that purpose?
I think the Nextcloud help forum is the wrong place to ask DAVx5 support questions. You should search the DAVx5 support forum for an explanation or ask the developers if you couldn’t find an answer.