I would not try switching feeders. ASF are incredibly hard to find, most buyers don't want to buy from someone who feed them because they are hard to find, people also don't want an adult snake that only eats mice because of how many one would have to feed. It is normal for BPs to go off feeding throughout the year. If he isn't losing a ton of weight I wouldn't think much of it, even though it's frustrating. Good luck.