Cases like this keep coming up in a few different lizard species. There is something up with the butterworms but since it's quite a rare event no one has been able to prove what's going on yet.
Silkworms raised on Mulberry farms feed have been tested and verified to have sufficient levels of Vitamin A, so try to include some Silkworms in their diet, they are also low in fat. Switch out your suppliments regularly and I use two different brands alternating them. You can also include...