I have been wondering for awhile why at certain times bubbles only appear in the last 30 seconds of cooking (we use a 7 min belt).

I know the younger the dough is, or colder it is the bubbles tend to appear about halfway thru, but i can not figure out why bubbles would appear right at the end as the pizza is browning up.

If you are using an air impingement oven this can be caused by an oven that is too hot or one that is not correctly profiled for your particular type of pizza, or baking on a platform that does not allow for uniform baking of the pizza such as a bright colored pan, disk or screen.
The first thing I would suggest doing is to drop the oven temperature by 25F and add 30-seconds to the baking time, let me know what happens.
Tom Lehmann/The Dough Doctor

We use screens, i will try lowering the temp and see how that works.