Your knees are sliding forward during the entire descent. Break your knees at the same time you break your hips, get the knees set early and then sit back behind them. Your hamstrings are pretty slack because your knees are forward and your a bit upright, so your likely not feeling a lot of bounce at the bottom.
That weight looks to be pretty easy. It will be even easier when you get the Hamstrings engaged. Knees are tracking really well out over the toes and no knocking as you come up. Good job overall.