If you are finding the following message on your parent product page: "There are no products matching the selection" even though the Child Category pages have products, most likely the "Show products from all subcategories." is not checked.
This can be fixed by going to the "Folder" or Parent Category and checking off the box to the right side *Show products from all subcategories:
Changing Show products from all subcategories will allow the Parent Category to inherit the Child Category Products as well.
Updated about 1 month ago