Customizer live view blank when plugin is activated

This image shows the blank Customizer “live view” https://www.dropbox.com/s/wgz1f6d9z84mae2/customizer-screenshot1.jpg?dl=0 Notice that the upper left tab shows “Loading” but it never loads.

This image shows the regular view when I deactivate the plugin https://www.dropbox.com/s/8kl0nkf7jq0e8f8/customizer-screenshot2.jpg?dl=0 Notice that the upper left tab shows the title loaded, indicating that it fully loaded.

Thanks for any insight.