Luckily he looks like he's still a healthy weigh, even with the loss. You can try a smaller size prey, maybe an adult mouse or rat pup instead? Mice have a stronger scent and might work. If not you can always try live, get him eating consistently, then try switching back.
yeah i was planning on buying him 2 live adult mice next feeding day. hes still active and healthy, now that i fixed his temps he looks more comfortable too.