CanadianGeorge, Nice stone! I have the same. I am no expert, but was having the same trouble with dough tearing every time I opened the dough. As I was looking at the bottom of your cooked pizza in Pic #2, it appears that the dough is like a patchwork quilt. It is all together now that it is cooked but I am wondering if it is one homogeneous piece of dough when you are stretching it. If it is not then perhaps you are pulling the section apart and the holes are the result. I hand mix, so I have no suggestion of your timing of the mixer, what did help me however was a longer more aggressive knead. Since I have timed my hand kneading to 7 min, I have yet to develop the holes with that process. Perhaps your dough, as currently processed, has a similar characteristic as mine did.
I am sure more experienced pizza makers will give a better answer.