Your knees are indeed caving in, and your grip is in fact fucked up. Widen the grip and get more hand on the bar so that you can maintain spinal tightness from the top down. The Man In Black behind you touched several of these work set reps, and you can't count them as done if he does this. What the hell was he going to do if you really got stuck? Curl your squat? Straighten out your spotting situation.