After upgrade, when I use the custom HTML "add to cart" link, the cart does not update, the mini cart does not update, and I am redirected to the empty cart URL with a message "The cart is empty."
Do you have edited the views "product / show_default" or "product / quantity" ?
If it is, try to save you custom views, remove the changes in HikaShop (dustbin in the view listing) and see if it's working fine.
Then adapt your code for the newest version.
