You aren't leaning over (breaking at your hips) at all as you start the movement. You need to lean over pointing nipples to the floor immediately. Your butt will then go back to counter. If you don't lean over the bar does not get over mid foot and it will not be balanced. You need to have the lean during the first part of the descent. You don't want to create it near the bottom. It is possible to have too much lean, but you are not in that camp. Lean over more.
You are losing tightness in the bottom and your back is rounding over. At the start of each rep, take a breath such that you bear down on your abs and keep your ribs down. Then hold that until the rep is done. Don't let any of the tightness go until you stand up the rep.