*Cannot* get that "Oven Spring"

I cannot, for the life of me (no matter what recipe I try), ever get the bread to rise that last bit in the oven. It always falls a bit instead.

It proofs nicely, but it just won't rise more in the oven. This time, I tried cutting little slits in the top (in case there was some sort of dried crust on top... even though I covered it with a clear shower cap), and I also preheated the oven for 45 minutes with a cast iron pan of water in the bottom of the oven, and a pizza stone. I placed the bread pan directly on the pizza stone.

The theory for oven spring is that the bubbles in the dough heat rapidly and expand. So there needs to be room for expansion (humid oven, no solid "crust" preventing it from expanding), and rapid heat transfer (pre-heated pizza stone).

It. Just. Won't. Work.

Any ideas?

P.S. - This is for gluten-free bread-making, but it should work just the same. All the recipes I try all assume that you'll get that oven spring. But I never do. Ugh. In case anyone is wondering, the latest recipe I have tried is this one: http://ift.tt/1vZLNGq