I am squatting quite light I think.
My max in competition was 180kg (396lbs).
The other day I was struggling with 140kg (308lbs).
I dropped it down in the end just so I could do some reps as I felt as if it it was pointless otherwise.
Thanks for your advice, although I'm not sure what you mean exactly about bracing properly and the tilting/hinging thing.
I do stretch the hips and hamstrings. The glutes I roll and stretch to some extent. I also do hip banded walks, and try to warm up that way.
How would I train my hip flexors - by hip thrusts? I found they really hurt my lower back last time I tried those.
I may try less static stretching and more dynamic stretching and actual warm up drills. Maybe that would help.