I'd just think that if something (add to cart) is not showing up with Woocommerce + Mystile (a Wootheme that supports Woocommerce) then adding another third-party plugin (Wordpress Mobile Pack) is probably NOT the way to solve it.
Dial it back to the minimum customization you absolutely need, then find the trouble.
Usually when someone says they can't get add to cart to show up with a variable product, it is because they didn't set up prices for each variation, but you get full functionality with the same variable product on non-mobile devices.
So the variable that is always there when it fails to show up is that it is being viewed on a mobile device, but only when it is a variable product? Is that right?
Which products are you having issues with specifically, would it be any of the dresses that have multiple sizes available, for example?