As I noticed, only the first edit in a contact is correctly saved. more changes throws xhr error “412 Precondition failed” with response:
<?xml version="1.0" encoding="utf-8"?>
<d:error xmlns:d="DAV:" xmlns:s="http://sabredav.org/ns">
<s:exception>Sabre\DAV\Exception\PreconditionFailed</s:exception>
<s:message>An If-Match header was specified, but none of the specified the ETags matched.</s:message>
<s:header>If-Match</s:header>
</d:error>
I also got problems with davdroid which got sync problems caused of missing etags …
I think thats somehow a problem of nextcloud or the contact app?!