Categories and Tags page not showing results

When clicking on a tag or category there are no results showing related to that tag or category.

Test environment:
http://onderwijscooperatie.getcolourful.nl/questions/

Tag page, this should show 2 questions:
http://onderwijscooperatie.getcolourful.nl/questions/tags/vraag/

Categorie paga, this should show 2 questions:
http://onderwijscooperatie.getcolourful.nl/questions/categories/categorie-1/

Thanks!