henrymcgillis recognized that if any parent of the cart element has a move animation on it, the cart modal will not show properly. However, you can actually put a move animation on the cart element itself and it will still work.
This was the fix for my project: I took the cart element out of the parent that had a move animation on it. I wrapped the cart element and my old wrapper div inside a new “clean parent div”. I put the same move animation on the old wrapper div AND the cart element itself. The new clean parent div wrapper SHOULD NOT have a move animation on it. It then worked properly.
henrymcgillis’ original post is in this thread:
Ecommerce Cart does not work with position: fixed