Child category links not working correctly in 2.7

I tried searching but couldn’t find anything relevant to this specific issue.

I’m running 2.7 and honestly not sure how long I’ve had this issue, but I’m guessing since I upgraded to 2.7. Anyway, my child category links aren’t working properly anymore. Here’s an example of what going on:

mydomain.com/parent_category/child_category doesn’t work anymore, “sorry, no posts matched your criteria”/

But this does work:

mydomain.com/child_category

This appears to only be an issue on the category archive pages — my posts still show up with the correct permalink structure, ie:

mydomain.com/parent_category/child_category/post_name

And this works as well:

mydomain.com/child_category/post_name

I checked the category setup and everything looks fine there. There child categories have the correct parent category listed and all that. Any help or suggestions would be greatly appreciated.