3D FlipBook - Category pages are missing

I have a flipbook with two categories Articles and Ebooks

but the View link in the categories page leads to a 404

https://newsignsmag.com/3d-flip-book-category/ebooks/

https://newsignsmag.com/3d-flip-book-category/articles/

The books are there on a page with the shortcode

https://newsignsmag.com/reading-library/