Is this toungue issue a sudden change, or has the problem got gradually worse over time?
Nutritional deficiencies (insufficient calcium or vitamins) are typically a slower, more chronic loss of tongue function. The chameleon tongue's aim may become misguided, or the tongue's reach gradually decreases until the chameleon can project it just a little or not at all. Missing the insects is often a sign of a deficiency in B vitamins (and sometimes vitamin A deficiency).
A good supplement or improved gutload containing these vitamins usually helps within a couple weeks if vitamin deficiency is the reason and the case is not too far gone.
Gutloading insects with leafy fresh greens such as dandelion will provide adequate Vitamin B (and of course other vits) to the diet. Another very good source of vitamins including B vits is Bee Pollen. Alfalfa is also a good choice for B Vitamins - its an easily digestible source of protein, B-complex vitamins, calcium, phosphorus, magnesium, iron and potassium. Many pastas are fortified with Vitamin B, There is thiamin in Sunflower seeds and wheat bran, B2 riboflavin in green leafy vegetables, fish, legumes, whole grains, B3 Niacin in cereals, legumes, seeds, green leafy vegetables, and Yams / sweet potatoes also have some B vits.
Other possibilities are mouth or tongue infection or abscesses, damage to the tongue itself (hit something sharp or cricket leg spines), parasites,...
There are a couple threads related to tongue issues already - try a search