Hi Benny,
Thank you very much for the details, it helps a lot!
I have found some issues with the configuration, and I believe I have corrected everything the best way possible.
First, the “All products” is a product category on your installation, which contains 7216 items. This was used as the default selected item, which I am not a big fan of – because by default everything belonging to this category is going to displayed (7216) – instead of actually displaying every single product (9918). The weird amount of items was caused by the combination of this filter with the others.
Instead of that, I have added the “select all” feature here. That will display the “All products” checkbox, when clicked, it will check all of the category checkboxes. I believe you could even disable this feature as well, because when no checkboxes are checked, then all of the products are displayed anyways
Another thing to note, that there are two categories excluded completely on the advanced options, “special order” and “special orders” – those have 8 items, so the overall results count is 9910 instead of 9918.