Ball pythons are known to fast even young ones but one thing I would do in that situation would be to get rid of the heat lamp and use belly heat. Heat lamps reduce humidity a lot, I would also try a smaller setup, maybe use a tub setup instead, he may be stressed from too much space. Are you able to feed him rats instead of mice? If he hasn't lost a lot or any weight he should be ok, try offering once a week instead of twice a week. He may just not want food lol bps are picky eaters.
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