Unable Customize Theme

I’m unable to customize the theme for my site. Specifically going to Appearance -> Customize, when the customize page appears nothing happens. The tab says: “Customize: Loading…”, the left pane loads(with nothing in it), and the site preview is just a blank white canvas. There is also no indication as to what might be wrong.

Note: I’m not sure if this is a plugin issue, there is an update for WPBakery page builder but I’m unable to update or activate it to update it.

The page I need help with: [log in to see the link]