Hi,
You could try updating to the latest version of HikaShop, but I guess you'll get the same issue.
Try changing the "Use AJAX when possible for add to cart buttons" setting of the HikaShop configuration and see if that helps.
If not, try changing the "After a product is added to the cart" setting.
If none of them help, all I can think of is an issue with the user session on your server. Try the same thing with a copy of the website on your local computer with xamp or wamp and see if that works. If yes, then the problem is really with the user session of the server and you'll have to contact your hosting provider support for help on that so that the session is not lost from pages to pages.