Why does my font selector show zero fonts?

I have checked on our demo and still works fine. Don’t worry, that’s not bug of the theme. In case you use the default font for the theme, the blank value as shown on your attachment will be selected. You can also deactivate all plugins to see if this resolves the problem. If this works, re-activate the plugins one by one and let us know if you find the problematic plugin(s). Maybe there is a conflict in plugins.
If you still face there issue, you can send me username & password of your site for further checking (via private answer).