Contact picture not connect with Faces on Photo
I think you may have hit the difference between the old handling of Faces &amp; the new. 

If your Face is tagged as 'john', &amp; 'john' is not in your Contacts list, it cannot find him.
If he's tagged as John Smith - john.smith@me.com then he can be found. 

The only way to associate the two is to click the name under the face in Photos, start typing the name, then pick john.smith@me.com instead of just 'john'.

Then when you go back to Contacts, it can associate the Faces selection with the appropriate Contact.

Here's an example using some Davids - the top ones are my 'Faces' as I already have them; underneath are the same people as 'Contacts' which is imho a lot less 'chummy' but how you must tag people before they will correctly link as Contacts.