Look at the differences between reps 4 and the rest.
On rep 4 your knees STAY where you SET them.
On the others, you SET them on the descent but that's not where they end up at the bottom of the hole.
Make all your reps like the 4th rep. You had knee slide on the others (not knees too forward, rather knee slide which has its own section in the book)
I'd get a 4" leather belt.
EDIT:
What Pete said.Knees are still wobbling a bit and you're still letting them punch forward at the bottom.
That said, that 4th rep is pretty good as a mental image to have.