Hi,
You can check the URL of the categories on that page.
You'll see that it has the menu item alias "hikashop-menu-for-module-115".
That's because this menu item is selected in the "menu" setting of the "HikaShop options" tab of your module.
This is the menu item that will be used to display the products listing of the category link clicked on.
So if you don't see the products when you click on a category and you have products in that category, it means that there is a problem with the settings of that menu item with the alias "hikashop-menu-for-module-115". So please check it via the Joomla menus manager, or select another products/categories listing menu item you know already works.
If you can't find what's wrong with it, you can provide a screenshot of the settings under the "products options" and "categories options" tabs of the menu item settings so that we can check them out.
And for the module on the left side, if you don't see it after you click on a category, it's probably because in the settings of that left side module, you didn't select the menu item with the alias "hikashop-menu-for-module-115" in the menu association setting, or that you have the "synchronize" setting of that module activated and it synchronizes with the selected category to try to display the sub categories of it (and thus if there is none, the module will be empty).