REV duplicated

[A Former User]

I am also having sync problems since Nexcloud 11, however there are no photos attached to my contacts. Initial sync seems to work fine from nextcloud to nexus but subsequent (which is really strange) sync attempts always result in errors. I see the REV thingy but no idea why this is happening or how to solve it

HTTP RESPONSE:
http/1.1 415 Unsupported Media Type
Cache-Control: no-store, no-cache, must-revalidate
Connection: Keep-Alive
Content-Length: 286
Content-Security-Policy: default-src 'none';
Content-Type: application/xml; charset=utf-8
Date: Tue, 27 Dec 2016 12:35:02 GMT
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Keep-Alive: timeout=5, max=99
Pragma: no-cache
Server: Apache
X-Content-Type-Options: nosniff
X-Download-Options: noopen
X-Frame-Options: Sameorigin
X-Permitted-Cross-Domain-Policies: none
X-Robots-Tag: none
X-XSS-Protection: 1; mode=block

<?xml version="1.0" encoding="utf-8"?>[LF]
<d:error xmlns:d="DAV:" xmlns:s="http://sabredav.org/ns">[LF]
  <s:exception>Sabre\DAV\Exception\UnsupportedMediaType</s:exception>[LF]
  <s:message>Validation error in vCard: REV MUST NOT appear more than once in a VCARD component</s:message>[LF]
</d:error>[LF]


EXCEPTION:
at.bitfire.dav4android.exception.HttpException: 415 Unsupported Media Type
	at at.bitfire.dav4android.DavResource.checkStatus(DavResource.java:318)
	at at.bitfire.dav4android.DavResource.checkStatus(DavResource.java:291)
	at at.bitfire.dav4android.DavResource.put(DavResource.java:202)
	at at.bitfire.davdroid.syncadapter.SyncManager.uploadDirty(SyncManager.java:317)
	at at.bitfire.davdroid.syncadapter.SyncManager.performSync(SyncManager.java:147)
	at at.bitfire.davdroid.syncadapter.ContactsSyncAdapterService$ContactsSyncAdapter.sync(ContactsSyncAdapterService.java:64)
	at at.bitfire.davdroid.syncadapter.SyncAdapterService$SyncAdapter.onPerformSync(SyncAdapterService.java:85)
	at android.content.AbstractThreadedSyncAdapter$SyncThread.run(AbstractThreadedSyncAdapter.java:272)

[rfc2822]

Please follow up at https://forums.bitfire.at/topic/1259/rev-must-not-appear-more-than-once-in-a-vcard-component/