Bug: Category counts in widget doubled on category pages

I am working on a site which uses a collapsing categories widget, showing the number of pages in each category.

On the home page, the numbers are accurate; but when seen on a category page, they’re doubled.

See here: https://citysecuritymagazine.com

And here: https://citysecuritymagazine.com/category/police-partnerships/

Look for the “Article Categories” widget on the right hand side.