Rich
Moving some good weight...one thing I want to see; the set-up! The bar appears forward of mid-foot and you are setting-up too far forward. Aggravating is your eye gaze, I would look a couple feet out, not straight down.
The FB forum is correct, you are lifting your chest too soon; probably bringing the bar back to mid-foot? Think of the movement as a push, "push the floor away," not "pull the bar." Notice how the bar stays away from the shins, bangs your knees, and then stays off your thighs until the movement is complete? This is not dragging the bar up the legs.
On the third rep you initiated the pull and then put the bar back down. What happened? You lifted your chest and dropped your hips, right? Knee extension starts, hips extension second.
Lets see a set-up; hook grip?