I think this is a different issue:
- this thread is about synching multiple addressbooks with Mac OS X.
- the other one is about syncing problems with Mac OS X. For the difference see this comment from @macnex : High Sierra address book does not sync and the according answer from user kfincei
I tried the fix from the other thread and it doesn’t solve Mac OS X not being able to sync multiple addressbooks. I also commented quite detailed in the according github issue: https://github.com/nextcloud/contacts/issues/399#issuecomment-468992259