Wheel bearing don’t generate heat until they start failing. Brakes work by creating friction which generates heat. If three wheels are cool and one hot, to me, that says that the hot one is the only one braking. (The OP stated that he had to increase the boost on his controller.) This could be a dangerous condition if you have to make a panic stop on a slippery road.
If it was my trailer, I would return it back to the shop and have them check the brake shoes for contamination. It could be that the service tech got some grease on the brake shoes of the cool wheels.