I have added an attribute (multivalue) in a M2 site that I have. I have linked some products with some attribute values. I have also included the attribute in the layered navigation. I can see the number of products in the parenthesis (on the layered navigation) that the values have but when I click on an attribute value then on the right it says that no products exist with this value.
As you can see from the screenshot Birthday says it has 20 products.