The bar looks to be about an in or so high right at your set up. It needs to below the spine of the scapula. Because of this, when you bend over, the bar is not locked in and moves up slightly. You relax your wrist to try to get it seated back down but then the heal of your hands push up causing the bar to want to move again.
Next time, approach the bar with a slightly wider grip. Keep your fingers open. Duck under and purposely have bar low on your back. Slowly adjust your back so the bar "slides" up. You will feel it catch in a shelf. Walk your hands in. Close your fingers and think about pinching the bar. Raise your chest and elbows and think about locking the bar in. Pin your elbows to your lats. If you feel your arms are loose, bring your grip in some more. Big breath. Stand up with purpose. One step back then the other. Eyes down, fixed. Back locked. Butt back, knees out, bend over. Reach down then drive up with your butt while keeping your back locked. Do not let the bar move. Keep it locked on your back and not in your hands.