The first screen dump shows my product listing (From Reports > Filters > Add Product
The Second is the report showing filtering by Category. As you can see by the results, I have Aus Mens Team Pants: L, Aus Dress Shirt : L & : XL etc. It also shows Aus Team Cap (which does not have a Size Variant)
The Third screen dump shows the same report as above, but when filtered by Product. As you can see, I have included Aust Team Cap and Aust Team Pants. So the result should show both Cap and Team Pants:L, but it only shows the Cap
The 4th Screen dump shows when I filtered by Aus Dress Shirt (which I had 2 Size orders L & XL) no products at all.