Sounds like the breeding season thing. In my house, 800 gms or over, which includes 1200-1300 gms, goes completely or partially off feed.

Our idea of breeding size is that--our idea. Ball pythons have a whole different concept of what is big enough to breed. They will breed at a far smaller size than most people realize, which is not an endorsement of breeding very small snakes. I don't breed any female under 1500 gms either because I want the female to have sufficient nourishment to produce eggs and keep her own body in good health. My smallest female breeder this year is a little over 1600. But just as some 10 year old girls are capable of becoming pregnant and reproducing, some ball python females will reproduce at an early age. My mojave female is just under 900 gms. I put her in a bin with a male just to see what she would do and pulled her out in a hurry because she was wiggling her tail in front of him and he was quite interested. She's a 2010 that is small because she was a mouser until I got her onto ASFs, so she is old enough to breed.

Snakes don't see things the way we do when it comes to "big enough" or "old enough." My guess is that your snakes that aren't eating are feeling their gender, to put it as politely as I can.