Long story short, I’m seeing some really strange behavior when updating fonts in the font manager.
If I go into the Font Manager, and change to a different Google Font, the builder will sometimes flip to a serif fallback font.
Sometimes it won’t update the builder at all, and will continue showing the old font.
Other times, the inspector will go completely blank.
I haven’t checked to see if this happens in production versions yet. In all cases, saving and then reloading the page will load things correctly.