I have contacts stored in ownCloud with PHOTO and other fields like X-GENDER and BDAY. After making changes to a contact on the phone those fields have disappeared in ownCloud. DAVDroid should keep fields it doesn’t know.
Duplicate of #118, please discuss there.
You could just export the events, (clean them up) and import them to your DAV server.
After reinstalling Threema (deleting account and Threema addressbook beforehand) it now seems to sync all contacts just fine.
Thanks - worked for me!