This feature is a narrow horizontal panel containing the add to cart button. It appears when you scroll down the page, and past the point where the normal add to cart button would disappear.
The issue is that some 3rd party plugins insert the extra product options into the same element as the cart button, and if there are lots of options, then it makes the panel huge instead of narrow.
I think in your case, it maybe better to remove it with the code in my previous reply.