Why does animated view start from wrong position?

Question

I'm using auto layout to animate the elements in a stack view. I've set the leading and trailing constraints, both with a priority of 1000 (required). However, as you can see from the animated gif, the stack view is initially attached on the left but not on the right.

UIView.animate(withDuration: 0.125, delay: animationDelay, options: [.curveEaseOut],
               animations: {
                   someView.transform = CGAffineTransform.identity
                   someView.alpha = 1
                   someView.isHidden = false
               }, completion: nil)