D-700 hot shoe issue
this has been common.
There seems to be a contact issue with the hot shoe and the foot of the flash.
Most often the heavy SB-900/SB-910 work loose the hot shoe.
Nikon replaces the hot shoe at a nominal cost.
Others bend(slightly) the spring contact in the shoe to make a stronger electrical connection.
I always adivse people to not put a shoe mount flash on the hotshoe.
I recommend using a SB-29 cord so the weight of the flash does not bend the hot shoe.
I have been doing this for years with all kinds of flashes and never had a problem.
I think I have a picture fo what this looks like, I'll look for it.