We had a similar experience disconnect warning that turned out to be a nearly cut electric brake wire, about one strand left. The wire was routed near the spring/axle u-bolt on the axle and the movement of the axle would short out the exposed wire giving the disconnect message. The cut was hard to see by just sliding under the trailer to inspect while on the road. The wire finally completely broke in two, giving a continuous disconnect message. Long story, short: check your brake wiring integrity and connections on your trailer.