I made some changes to this page and now I’m getting an error only on certain listings.
I’ve narrowed it down to the some extra lines of code (pasted below) that are being added to those with the error.
It’s not valid HTML to put a block element (e.g. div) inside an inline element (e.g. b).
The main reason for the issue isn’t the invalid use of a div tag inside a b tag however. You’ve used that on all the listings as far as I can tell. But you’ve used it in a different place on the broken listings. And so the col-sm-3 section-footer class on the child div creates an unusual layout.
So you need to remove the b from whatever system you use to create the listings, rather than try to fix this with CSS.