Hi,
Thank you for your feedback and the details on the issue.
It comes from an improvement we added in the 6.0.0 to display a message when no products are found in a category.
And on your link there are no products displayed on the page as only the sub categories have products, not the main category of your menu item.
I agree that in such case, the message should not be displayed. I've made a patch to handle this.
Download again the install package of the latest version of HikaShop and install it on your website and you'll get the patch.