Hello,
If I take a look at a product page source code, I cannot see any reference of the URL like the one you had.
The "add to cart" right have its right format
href="/men/product/updatecart/add-1/product_id-6322.html"
And regarding the cart module, the "return_url" parameter is right sent by POST data and not in the URL.
o.xRequest("/men/product/cart/module_id-759/module_type-cart/tmpl-component.html", {update: el, mode:'POST', data:'return_url=aHR0cHM6Ly93d3cucmV2ZWxwcmludHMuY29tL21lbi9wcm9kdWN0cy9sb3ZlLXlvdXJzLW1lbi13aGl0ZS10ZWUuaHRtbA%3D%3D'}
So, I don't know from where these URL are coming from. But it might be old/previous URL which are still referenced somewhere.
Regards,