Multiple Taxonomy Filter – Vertical not showing

Hi! So I wanted to use the Multiple Taxonomy Filter – Vertical on this particular page, since I have categories for books as well as tags for the authors. But the Filter won’t show on the left side. If I choose a horiontal display of the filter, it works. Since I have consistently used the vertical filter on other pages, I would love for this to work here as well. Do you have any idea what could cause this issue?

The page I need help with: [log in to see the link]