I really don't know what the issue could be.

I can say that my BRB when I got it I was told that the previous owner had a terrible time trying to get it to eat. It should have been taking a medium rat but it showed no interest in them as live or f/t. I eventually found that it would slam a small rat so I stuck with those for a few months and then I moved it back to medium rats and have not had it refuse since. Maybe try a smaller rat and see what happens.