What is your ankle mobility like?
Your heels are moving in to create slack within the system to allow you to squat.
Think of your weight being through the arch of your foot vs in your heels.
The issue could be at your hip.
Squat Quick Test: Is it your Ankles or Hips?
Foot Position Test: Breaking Diane
Case Study: Tight Ankles = Bad Squatting
Episode 303: Going Around The Ankle at MBSC
Episode 285: Sliding Surfaces; Ankle Range of Motion Case Study Part 1
Episode 285: Sliding Surfaces; Ankle Range of Motion Case Study Part 2
Yes, you shoulder were in a better/more stable position so other elements found a better place as a result.