#578 is caused by https://github.com/owncloud/contacts/issues/581 which is present since at least OwnCloud 6.0.3.
Please follow up in the issues mentioned above.
I use DAVdroid 1.6.4-ose on a Huawei P9 Lite with EMUI 4.1.1, Android 6.0.
Because I had trouble with the sync, I added a new CardDAV account. Now, some days later, I don’t now why (sync every 1440 minutes in DAVdroid options), the sync works again. If I take a closer look to the contacts now, both, the old http-CardDAV and the new https-CardDAV account are listed under every contact entry. The http-CardDAV account has the name affix “oA” and the https-CardDAV the name affix “Aw”.
What does “oA” and “Aw” mean?
Thanks for your patient help!