Topics with a gap at the top of the page

This is something that has been happening seemingly randomly for a long time. Some topics have a gap at the top of the page while others start at the top as expected. Here's a side by side comparison:

The headings for both of these topics use the same style and they use the same css file. I don't see anything in the html that would explain this, as far as I can tell. Anyone have any idea why some topics have a gap at the top?