It's a 2012 model- so like everything else these days, I'll bet its got some electronic switches and valves, and something has gone (even further) south. Probably a flow director valve with a safety switch that shuts off the water flow to the heater when there's no water in it, so as not to burn up the water heater.
You need to get a schematic of the electrical and water heating systems, probably from the manufacturer of the water heater. Is there anything in the documentation of the camper along those lines?
Also need to find a more knowledgeable RV repair outfit. . .