[Steven Zahm]

@ Harald

Actually doing this is valuable time spent… for example, what if the issue is actually two plugins conflicting when the Customizer is loaded or if a combination of plugins and themes.

What does not make sense… the Customizer should load just fine with out any other plugins and the default WP theme… but you are saying it does not? If so, that would indicate a new and unknown issue that may be unique to your installation. To investigate further, I’ll need an admin login so I can debug further.