Squat form check

[Aaron Wachter]

I would appreciate any feedback on my squat technique. The videos are of my first and second sets at 340x5. I am especially curious about my lower back position. I feel like it goes into flexion at the bottom which is very concerning to me as I have had a disc related injury.
YouTube
YouTube

[Jeff Illingworth]

You're a touch shallow. You are also a little too vertical.