After cadaver bone graft with implants is there any reason that there would be bone loss two years later?

there r many reasons for bone loss. it is difficult to say anything without seeing xrays , so its my advice to update xrays.

Without before and after xrays it's impossible to give you a specific answer. When implants inserted and a bridge is placed it is not uncommon to lose bone in the site with no tooth and around the implants. The rate at which this occurs varies from person to person. I'm not sure why you should go see the endodontist as this would have no bearing on bone between the implants. 

Hi:Unfortunately without an xray it is difficult to give you accurate advice.  Please post photo and xray of the area.Best,Dr. Maddahi