Hi Iksan
My guess is your shin is too vertical. You could let your knee travel about an inch over your foot. I believe you had another video where you used a tubow?
When you breathe you relax the top part of your back.
From the side view
The bar is not over mid foot when you start, out is that a recording angle? You wiggle with your feet in the beginning of the second set to feel mid foot I presume. But I'm thinking your on your heels. I think you should have a bit more forward angle from your ankles, shins, back. A complete straight line. Now you have a straight line with your legs and then a bend in the hips to get bar over midfoot. Or am I mistaken?