Hi please see the video here https://we.tl/t-whXbj7XpPn
I have tested it using your demo link.. but the issue is still the same.. it looks like on a desktop it works with 1 click because the mouse hovers over the button before we click but on the phone the first tap behaves as hovering over the button then the 2nd tap is to add it into the basket.. which adds that unnecessary tap / slowness to the experience.
Hope that helps
Best regards,
Kevin