hard to tell from that angle if you are hitting parallel or not.
i used to low bar squat like that but i found it really hard to keep the elbows under the bar. with bar that low the arms support a lot of the weight and it absolutely killed my shoulders and arms. obviously an issue you are having. as you drive out of the hole your elbows are drifting back which loosens up the upper body. the lower back loses it's arch and rounds and the weight pitches forward. i bet if you go much higher that you will lose the weight forward.
on a positive note it looks like you are doing a good job of pushing the knees out.
i would suggest giving a high(er) bar position a try to allow you to more comfortably get your elbows under the bar. forcing the elbows down under the bar locks the entire upper body into a tight position. it locks the lower back into an arch and keeps the weight over your hips. then all you have to think about is forcing the knees out until you hit depth and then drive out of the hole. the upper body should stay in the same position throughout.