For some reason when you add to cart or if you click the checkout button in cart, it takes you to /search?q=&options%5Bprefix%5D=last&form_type=product&utf8=%E2%9C%93&id=37839505653948&quantity=1&add=/
I've spent a long time trying to figure this out and all I have found so far is that most of the forms on my site are missing the <form> tags. So if I look on an older backup of the site it works because the buttons are wrapped with <form etc...>. I've replaced the entire product-template.liquid file with the liquid from the working theme, however this still hasn't fixed it.
I did the same with theme.js, and theme.liquid.
Does anyone know why on earth there would be logic to look for "form" tags and remove them??? it looks like it's being done prior to page loading also.