Hi,
1) Seems like the responsive minified stylesheet is corrupted. Have fixed that for the next pending updated. If you switch performance options to off in Theme Options => General Options => Performance Options does that change the display?
On small screens the thumbs should be below the slider.
2) Is this a variable product or simple product? Variable products do not use Ajax to add to the cart currently.
3) Please add this to Theme Options => Custom CSS:
.product .cart-overlay .add-to-cart-wrap {
display: none!important;
}