Check connections to the canbus in the nearside rear corner behind the upholstery.
Was it aftermarket or came as standard with the car from the factory?
There is a cable that runs along the near side and plugs into the back of the radio somewhere, to give you the video on the screen.
Check connections to camera itself in the boot lid behind the cover.
Could be a broken cable somewhere, the part that moves with from the boot is a likely candidate.