Hello everybody from NOPCOMMERCE team! Your product is wonderful. Congratulations!!!
Let me tell you about error in Filter by Attribute. The problem may be is in application.
There is a category in my e-commerce which name is numeric. In my case CategoryName is 620 (from HP -> 620). When I choose this category I can not look at its products, because the products are filtered by Filter by Attribute, which SpecificationAttributeOptionID = 620 (table Nop_SpecificationAttributeOption). I couldn't remove Filter by Attribute in any way. Not allow filtering in Product details in Category 620.
I resolve my problem like change Product Category Name.
Good luck,
Elena!