Suprised nobody has answered you yet!
It looks to me as if you are looking in the mirror while squatting. If you are, stop. Before and at your sticking point, your hips are driving up while the barbell is not moving at all. My guess is if you were to put a heavy weight on your back and fail to squat it, that you would fall forward. This means you likely have a weakness in your mid/upper back. You can strengthen it by deadlifting heavy or doing heavy barbell rows. There are other ways too, but I think those would be the simplest.
Looking up instead of looking in the mirror will also help you drive your back into the barbell.
You are also getting forward in your heavy squats because you are breaking at the hips and knees simultaneously. This is placing your knees way far forward over your toes and placing more of the load on your knees as opposed to your posterior chain. You would be able to squat heavier almost instantly if instead, you break at the hips first like you are doing a romanian deadlift. Then, sit back like you are going to sit on a chair. While sitting back, spread your knees with your hip abductors and drop down in between them. Not sure if that makes any sense, but practice it and you will know what I mean.