Word count in individual documents not updating

So I have a scrivener project i use to keep all my writing odds and ends. For some reason, several documents display a word count and character count of 0 at the bottom of the page. This only seems to happen with documents that are older; when I create new ones, the word count updates as expected. I’m running version 1.9.7.0, if that helps.

Here is a picture of what I mean.

gyazo.com/0364d9c5251b1ab75628472b1f796b3d