I like how Amy added in the supplement containing preformed vitamin A. I have heard that although some supplements use beta-carotene as a safe source of vitamin A (since preformed is fat solubale and toxic in excess), amphibians cannot fully rely on beta-caroetene and need some preformed vitamin A in the diet. They would likely receive both due to beta-carotene from algae at the tadpole stage and plant matter from the gut of insects, then some vitamin A would be from the occasional small veretebrate taken.

If you were using a supplement with only beta-carotene and not feeding pink mice, whole fish or fish oil on the insects, then short tongue is would still be a real risk.

It could also be a lack of D3 in the diet or an underpowered UVB lamp. The 2% lamps
generally recommended for amphibians are completely useless when used over a screen top as this halves the already low output. Although, many keepers have kept toads without. Just make sure enough D3 and calcium is given. Mealworms are very poor in nutrition so should be gutloaded with a commercial high-calcium diet or with dusted calcium supplement and occasionally multivitamin dusted for vitamin D3 and A. I would use earthworms, suppmented crickets and roaches as the main diet.