I had a ball that had tape worm. He shed every week and actually got water blisters on his skin. The tape worm stressed him out so much. I'm not sure if this is common with parasites or not. But pictures of this skinny snake would help. It's hard to say it's losing weight if you don't have scale. The human eye is so imperfect. Unless you're seeing a huuuuge difference. Please post pictures. My 500 gram ball python was taking 60 gram rats just fine. We don't power feed. We feed a little smaller than the thickest around their bodies. I know plenty of awesome breeders who do the same.

Also I've found and heard that snakes grow more on live rats rather than frozen thawed. Is this the only snake eating f/t or are all your snakes eating it?