Tapioca pizza crust is undercooked?
This seems to be a leavening problem. Normal pizza crust is leavened by the interaction of yeast and gluten, you admit you don't have any of those here. 

You can of course try making a chemically leavened crust (with baking powder), but it will still have trouble working without gluten, that's why gluten free flours usually contain gums. 

From your description, I can't tell if your "flavored flour" has leavener and gums. If it doesn't, look around for a recipe which uses tapioca flour from scratch and has those, and use this flavored version instead of the pure one. If it does, then it is a trouble with the balance of the two, plus the added ingredients. Are you sure you are making it exactly by the package instructions? If it says to use water, the fat you are adding could interfere. 

In the end, it is quite difficult to get a gluten free dough to rise properly. You can experiment with gums and leaveners, but expect a long process of tweaking until you get it right.