Hi,
It looks like the views of HikaShop have been customized in your template. So It's highly possible that it comes from these modifications.
Try to switch to the protostar template and see if the system behaves properly.
If so, then it's indeed what I'm talking about.
In that case, open the folder templates/YOUR_TEMPLATE/html/com_hikashop/product and rename them one by one until you find the view file where the modification messing up the add to cart button display is. Then, you can look in the file for the exact modification or contact your template developer (if it comes from them).