I don't want to come off as mr. nitpick every time I see your back squat, but I have to comment in hopes it will help your form.
Your descent looks good and everything looks good as you rise up until you are hitting the sticking point. At this point you really need to work on keeping the shoulder blades retracted tight and getting the chest up.
With the coaching I've been getting and having tested my max a couple weeks ago I definitely can see what happens if the upper back tightness is not maintained enough.
If your upper back is rounding over with 315 imagine what would happen with 400. Keeping the upper back arched is paramount. Before the national level and former 242lbs class champ helped me get my squat form back because of patella troubles I tested my squat max and even though I got the weight up I lost the upper back arch coming up like you did and I was lucky I didn't bomb out.
Get the upper back really tight. Focus on keeping that tight and the elbows pointing down and pointing them forward on the sticking point. Go straight down. Don't worry about your lower back because if your upper back is arched hard and you are looking forward with the elbows mostly pointing down then when you drop into the hole you could take a snap shot and it would look perfect because the back from the ass up should look like a straight line, not over arched.
Anyhow, I won't post anymore squat critiques in your thread, but I hope you don't take this the wrong way. You're doing excellent man. Keep up the good work.