Post Grid not showing Category Listings

Hi,

I am using Post Grid Pro, filterable grid.  The blogs are not shown when  I click the "category" listing.  For example, on this blog page,

Dinosaurs by Stanley

if you click on one of the categories listed on the right sidebar, it pulls up an empty page like this:

https://origami-resource-center.com/category/animals/

When you move your mouse over the page, you see the pointer icon which suggest that the posts are present, but invisible.

Hope you can help, thanks!