I have and Object A. A has a master detail relationship with Object B, B also has a master detail relationship with contact. On object A's page layout I've added a related list for Object B. In the related list I'm trying to display Contact: First Name Contact: Last Name. In my sandbox, which is in classic mode, the values and headers for First and Last name display fine. But in the full sandbox, which is set up for lightning, the values and headers do not display from contact. I've checked the permissions on contact. When I click into object B, I can see the contact's Name. I can click into the contact and edit it fine, no permission issues. It just doesn't want to display on the related list. I have no idea why.
EDIT: I believe it is tied to Lightning. The related list displays fine when I'm in the standard console app in the Full sandbox.