Hello Ernest,
I understand your above logic, and not successful in my try and error testing.
I backed to normal situation and tried to use “Category” to filter : below is my case
Post1) selected 2 categories : M size & CAT1
In Related post pro, I remain the category CAT1 in left side and EXCLUDED all in right side. YES, I can see that CAT1 posts, but it also shows another “Page” records. Can you advice how to exclude type = PAGE (in wordpress left menu) ?
Regards
Justin