Hi,
The issue is with your template, not HikaShop. On small screens, the left sidebar is invisible but goes on top of the main area. And thus, when you try to click on something of the main area, you actually click on the sidebar area and it doesn't do anything.
You can try adding such CSS to your website and that should fix the problem :
@media only screen and (max-width: 800px) {
.rt-grid-4{
display: none;
}
}
I would however recommend you to contact your template provider as there may be a better solution or maybe they'll have to modify their template to fix that behavior.