Customizer not loading

I've emailed support a screenshot of what may be causing the error. It's an outdated core plugin 'ivan-demo-overloader' apparently. This is what's preventing much of the code to not render on the web pages but not sure if it's preventing customizer from working, though.

So when you disable that plugin does the customizer work again?

nope

Ha, I just asked the same question via email. Let's stick to this topic so we don't get confused.

So deactivating that plugin doesn't change anything at all? Any reason you singled it out?

I referenced it earlier in this thread "I’ve emailed support a screenshot of what may be causing the error. It’s an outdated core plugin ‘ivan-demo-overloader’ apparently. This is what’s preventing much of the code to not render on the web pages but not sure if it’s preventing customizer from working, though."

This plugin has been removed to my knowledge (at least it's not displaying in plugins, I also removed the files). It was a core plugin with the theme 'copro' but is no longer being updated and was causing issues rendering shortcodes on the webpages. So I'm trying to use GP and rebuild the pages using a lighter/quicker theme etc. However, I can't say for certain whether this is causing the customizer of other theme's to not load. I already sent wp login by email for you guys to take a look at. It does seem to be something connecting to the current 'copro' theme that's causing the issue because the current theme customizer loads but no other themes customizer appears to work.

The URL you sent via our contact form doesn't seem to be using GeneratePress? I took a look anyways and the Customizer loaded fine for me in Chrome.

I deactivated it and was using the previous child theme 'copro'. I was having several issues concerning that theme and some of its associated plugins. When I attempted to load GP customizer in Chrome I got this -
Fatal error: Cannot unset string offsets in /customers/8/3/d/preferentialpassports.com/httpd.www/wp-content/plugins/mega_main_menu/plugin_framework/extensions/mega_main_menu/menu_options_array.php on line 13
This was the first time I got that message. I deactivated the plugin and it seems to work now.

Awesome, glad you found the problem plugin :)