Jamie, I'm going to throw out a bunch of theories here, because there's a few odd things going on. Everything I'm asking is important, so please try to answer all the questions to the best of your ability.
Is this exactly the same flour you were using with the clay oven? If it was, how long have you been using it and has it always been consistent? Did it ever give you the yellowing that you're getting now with the clay oven? Is this a reliable flour miller and distributor? Is there any chance the flour got wet or wasn't stored properly?
Do you have other bread flour options?
Please list the ingredients of the flour.
Are you testing the hearth temps with an IR thermometer?
This is a brand new oven, correct? Have you cleaned the stone hearth? Are there any odors coming from it during the pre-heat?
I know it's coming down to the wire here, but, in order to understand what's going on, photos of the oven would be huge help. A close up of a stone would help, especially if you can lift the stone out and show the thickness. A shot of the broiler element is critical.
When making pizza dough, when you combine water and flour, it should be stirrable for a few seconds and then become impossible to stir. At the point where it becomes impossible to stir, you knead it. If a lower hydration dough isn't rising properly for you, we need to look at other factors, such as gluten development, yeast quantity, salt quantity and fermentation.
Hydration is critical for oven spring, but you can always have too much of a good thing. This is a dry flour- perhaps as much as 3-5% less water than American flour. 12% protein flour should have an absorption value around 60%, though, so to compensate, you probably shouldn't be that much north of 65%.
Are you located on a mountain or at high elevation?
We need photos of the cheese. Both pre-bake (shredded) and post-bake, as well as a shot of the cheese in the packaging. Is there a temperature where the cheese will melt and then bubble?
Pizza diameter? Dough ball weight? Sauce quantity per pie? Cheese quantity?