The Hinge is fabricated with double yoke type arms welded onto a tube into which the hinge bolt fits, the bolt going through a welded bracket top & bottom which are welded to the body tube frame (A pillar) these arms then are then bolted onto brackets which are welded onto the Front tube frame of the door!
It may be that the fixings have loosened or worst case the brackets fractured, there could also be some wear in the pivot hinge bolt, you will need to expose the hinge area to determine the problem, a good body shop should be able to deal with it & re-hang the door into the frame!
Robin