Tapioca pizza crust is undercooked?

So I’ve been having issues with this GF tapioca pizza crust. I like the crust a lot because it’s allergy friendly (no yeast/soy/gluten/nuts/anything really) and actually doesn’t taste like rocks. Problem is, I can’t tell why the crust is coming out undercooked every time.

The box recommends 450F in a 14" circular pan for 15-18 mins or 7 mins to cook the crust, 7 minutes to cook with toppings. (Note: it’s not a premade crust, it’s essentially just flavored tapioca flour; I add eggs, milk and oil to it).

The first time I made it, I put the crust in for 7 mins on a metal sheet at 450F, and then cooked it until the desire time. Upon seeing it unfinished, I put the combined crust and toppings in for 13 extra minutes (so ~20 minutes totally). The results were the same and I would have kept it in longer, but the cheese was starting to burn.

So I said okay, let me change it up. Today, I used a glass pie pan (I think a 12" one), cooked the crust for a full 10 minutes at 425*, and then cooked it with toppings for another 10 minutes at 450. Exact same results. I figured this could be my fault, it’s hard to guess the time difference of 25 degrees, so I said screw it.

I put it in the oven for a whole 16 minutes at full 450 degrees, no luck.

My question is then:

1. Is this actually undercooked? I assume it is, but I’ve never had actual tapioca bread before, so I don’t really know. But in the first image, you can see how the bottom looks clearly done (aerated and structured), but the middle is slightly mushy, translucent, and (hard to tell from the lighting) significantly darker than the rest of the crust.

To best describe it, it’s a thin, shiny line that looks like the texture of a gummy bear.

2. Since I assume it is undercooked, where am I going wrong? Do I just need to stretch the dough out that much more? It was already tearing both times, so I figured it shouldn’t be any thinner than it was. I don’t think it’s an oven issue – we did have some uneven cooking year and a half ago, but cleaning it out seemed much better now.

Do I just need to ignore the box and just stick it in the oven longer, maybe at 400 degrees?