I looked at your data. In the butterflies category, there is only one product listed in the database, which is why it displays only one product.
In the table hikashop_product_category, if you search for the the category_id 20, there is only one result which is the link between that category and the Reef product you have.
So, could you precisely name a product of that category ? That way, I would be able to check the other way around...To see if that product exists without a link to the category.
How do you add the products ? Do you use the import of a CSV file ?
