Did any of the vets mention the possibility of hypocalcemia? The early symptoms are paralysis of the tongue .
Do you lightly dust all /some feeders with your 4 part supplement schedule or quite heavily coat them
If it is a tongue bacterial infection maybe in sheathing hopefully the broad-spectrum antibiotics are effective on it.
But you might need blood work done to check calcium levels if tongue doesn't heal up after the course of antibiotics &maybe insist the exotic specialist examine your chameleon just to be sure the general vet missed something
The vet found "trauma to the tongue on one side". Its not D3/vitA/MBD/husbandry issue. Either the feeder got in a few good hits on the tongue, or the cham did it himself while catching/killing (he is one of those that like to bash the feeder against something).