I have a workout buddy who was having the same problem and the problem went away by keeping the bar midfoot.
-Make a small reset 5-10 pounds to your worksets
-Take the squat stance with symmetrical feet positions
-Shift your weight on your toes and then to your heel and then back so the weight on your feet feels balanced and equal
-Really focus on keeping the weight balanced on your feet throughout the whole movement
-LOOK DOWN to get on the hips to draive
Try these and see if it helps.