My 2016 Nexus 32SC came with an Atwood on demand water heater. The problem I've had is insects getting into the vent for the diaphram switch that is used to determine that the blower is running. For some reason they like to crawl in there and plug up the switch port with a mud-like substance. When it was partially blocked, I experienced intermittent operation like you described. When fully blocked, it would not light at all. I recently put a piece of adhesive window screen over the vent opening and it seems much better. Will know more after our next trip.
