Hard to see in that video, but a couple things - first, that clean pulled you forward so you were already set up for a miss like that no matter how well you racked it. Pause the video right as the bar reaches your knees and look at your position - too forward.
I think what's happening is that you're opening up your grip a little to soon, and that's allowing your body to separate from the bar. You can see that you pull it right in close along your chest, but as your elbows begin swing around, your hands open up and all of a sudden this space develops between the bar and your shoulders.
Also, I think your rack position just isn't solid enough - a good rack will withstand a bit of crashing like that - but the moment that bar isn't delivered perfectly, your hands pop out. That suggests that even with the bar settled on your shoulders, that position is just waiting to explode. More front squats, and a lot of emphasis on driving the elbows up - make sure you're not pushing up with the hands.