Hey,
It sounds to me like it could be one of two things: scale rot, or blister disease, or dermal burn from lying on a hot pad, while soaking or lying in the sphagnum moss. Are you keeping the moist hides over the hot spot? If so, I would move it to a cooler side of the enclosure, as hot areas and over wet conditions lend to this condition developing in young animals. Reduce the number of hot spots and recheck the temperatures over the surfaces, where the snakes hot spots are located, and reduce the amount of moisture in the moist hide. If the snake is urinating in the moist hide (usually after a meal), there is a very good chance that he or she is lying in it, and this too, can contribute to blistering in some juvies less resistant to blistering.
Remove the moist hide for now, and place him/her, on a clean layer of newspaper or paper towel, and apply a topical antibiotic to the area (Neosporin), and keep the cage dry till it heals. It will go into a shed and the blistered areas will eventually heal, but you have to make some adjustments to your snakes cage condition and address some husbandry issues. All will be well. Good Luck!
-Angel
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"Until we lose our self, there is no way of finding our self."
-Henry Miller.