Vz Galaxy s7. Same issue. Tested multiple apps and multiple headsets, all same issue. So far doesn't happen while screen is on, and enabling always on feature doesn't help.
Ditto on my S7 - you can sync Google+ photos (Those are the only contacts that show up with photos), but even with sync turned on in FB messenger, no sync occurs.
I knew it would break within 6 months when I first upgraded from the S4. And sure enough, today it broke off.
Granted, the design is TOTAL garbage, and chances are I'll be leaving Samsung after the 5, but still.....