Blog category filter working on main page but NOT on post list page.

Hi all, my blog features a main page with all posts, and the category links to filter the posts, this works perfectly.

However, I have also two dedicated pages for 2 of the categories, where I have set up a post list and selected the corresponding category. This was working perfectly fine for the last couple days, but now it shows no posts.

What I find very strange is that the filtering works on the main blog page, but not on the post list.

Can anyone help?

Thanks in advance!