Tony,
Check the cabling at the back of the unit. It sounds like one of the cables is loose. There should be four cables attached. One for the backup camera and three alternates...mirror cameras, inside camera etc. If one is loose, the movement of the coach will not allow a good connection. When stopped, it does. Find the 'brain' and make sure all cables are pressed in tight. If it's happening on both the front display as well as the one in the bedroom, then it's probably wiring at the 'brain', otherwise it's probably the wiring to the front display.
I found it a good idea to get a package of zip ties from Home Depot and zip tie all my wiring about every 8-12" throughout the coach. This prevents this type of incident. Loose or hanging wires are simply wires waiting to fail....good luck, hope this helps...Dennis