You are still effectively squatting "high bar." Look at your back and see how vertical it is. We don't want that. Lean over more on the outset of the movement. Look at a point 4-6 feet on the floor in front of you. Point your chest at the floor. Proud chest, too. Less elbows.
Beyond that, you are dive bombing these, i.e., falling into the bottom. Further your knees are squishy through the whole movement. Do you see how the punch forward at the bottom? When you start, shove your knees out, get them just past your toes, and keep them there.
You are also not tight at all and going too deep, thus your low back flexes and likely the reason for the discomfort, combined with the excessively fast descent.
Loose the deck shoes.