Hey I am currently experiencing this issue and I have not been able to resolve it yet.
The gap displayed only shows on mobile view for one of my products and not any of the others. I have deleted all html code In the product description, have tried cropping images to fit the gap which does sort of fix my issue, however their is still about one scroll worth between the top of the product page to the add to cart, which is far too much (especially because for my other products there is no scrolling between the top of the product page to the buy button).