I am going to go out on a limb here and say your vet sounds like they do not know what they are doing. BPs go off feed all the time, they are notorious for it. And I would think any competent herp vet would know that... I also find it difficult to believe a BP would go into anaphylaxis over a dewormer. I am more inclined to think it was overdosed and what you were seeing was toxic effects and the vet pulled a CYA with the anaphylaxis excuse.
There is no real need to deworm a CBB ball anyways...
As for why your animal went off feed... As I said, they just do sometimes. I had an animal go off for 4 months. Then he started eating again like nothing had happened. I have heard of them going a year. So long as they are looking and acting healthy then just keep presenting with food on a regular basis. They will eat when they are ready