Hi,
In the HikaShop configuration, you have a setting "Synchronized add to cart". Please make sure that the option is turned off.
Also, I can see you have a build of the 4.5.1 from a month ago, so you don't have all the patches we published since then. If you still have the issue with that setting properly deactivated, please download again the install package of HikaShop on our website and install it on yours.
And if you still have the issue, then it might be linked to a view override so please check if you have the issue with the default Joomla template.