Do you keep him in a rack? I had some snakes show very similar sores on their lower lip, either on one side, or symetrically on both sides. I consulted a veterinarian, and he told me that he saw very similar sores on animals in another collection. He said that the other collection was also kept in tubs in a rack, and that the problem ended up being that there was enough of a gap between the tub and the rack that as the Ball Python tries to explore and escape, it rubs a sore (or two) on the lower lip. When I checked my collection, sure enough, all of the snakes with the sores ended up being active snakes in tubs with a small gap between the top of the tub and the rack. I have shimmed under the front of those tubs and all the sores have healed up.