One brake shoe dragging

We have a new to us 2016 320 with very low miles. Have towed 500 miles using our Prodigy RF controller, no problem. Leaving a campground yesterday, the trailer brakes locked up when we were going maybe 8 mph. Adjusted the controller to a lower setting, and all seemed fine. Then about 80 miles later, we heard a squeal when starting from a stop, which disappeared. Thought it was from another vehicle. When we reached our destination, the entire wheel and rime was HOT. We were very lucky not to have a blowout or fire. It isn't the wheel bearings, as i always check to see if there's a hot hub when we stop for gas. I think this was perhaps the brake on the driver side staying engaged. We drove the rest of the way home w/o the electric brakes (disconnected the RF controller. We still had lights, etc., just no trailer brakes. ANY IDEAS?? Thanks