Low back position on squat - YouTube
The lower weights look terrible, it's difficult to get the movement right when the weight feels really light on my back.On the second 100kg set, I tried out being a bit more upright and it felt much better on my back, but of course that makes my knees go forward too much, so I only tried it out on that set. I had pain doing 140kg and 150kg, about the same as the 160kg set last workout.
140kg deadlift - YouTube
I also did deadlift which still caused pain. I have issues on the concentric, from the floor up until the barbell reaches my knees.
Something I've noticed is after my sessions I have some tightness and very mild pain deep in my glutes and the sides of my hips which radiates a bit down my legs. It's not intense at all, even on the days that my back hurts a lot, so I don't know to what extent that info might be useful.