New Contacts in ios 11.4 not synct with contact app

Hard to say, do you see errors on the phone? The logs in your post don’t really reveal on a first sight. The put command from your phone receives a 204 code, which means it received and processed all data but no answer is given. Not sure if that is normal.

For the rest, there is first an error via normal access, then the authenticated request is successful.

Can you try one of the demo servers, if you can replicate this behavior?

And on the previous iOS version it worked?