Missing Site Stats bar graph

Here’s a weird thing — since I upgraded to 4.0.1, the site stat bar chart on the top of my page (when I’m logged into my site as the admin) is missing! I just get a ? box denoting a missing graphic.

I tried deactivating and activating Jetpack, no change. It’s still missing.

I miss this feature — anyone know how to bring it back?

Thanks!