I thought the target for mozz was 5.2-5.4? I tend not to use pH but heat a scrap of curd to stretch test it at 30 min intervals.
When I've rejected other raw cheeses during the make (eg blow), I recycle the curd to mozzarella and I have seen that slobby texture you have in the lower picture. I think it's when the curds become too acidic.
I have a trick for this that sometimes works: mix a little bit of bicarb (1/4 teaspoon for curd from 1.5l milk) in to the hot curd, let the curd cool down to room temp, then try again, I suggest heating in the microwave to make sure the curd don't fall apart in the hot water.