Why is the sidebar wrapping under the blog posts only on home page?

Hello all,

I am confused about what is causing the side bar to wrap under the blog posts on the homepage of this site. It just started doing this.


The sidebar behaves correctly on the blog page:


The side bar also behaves correctly on a blog post with a sidebar:


On the home page when any pagination link is clicked, then the sidebar behaves correctly on those pages.

Is this a CSS issue or is it something else at play here?

Any insights appreciated.