Missing Theme Options / Customizer or UX Builder
If you get a blank Theme Options screen or have problems opening UX Builder try these steps:
1) Increase memory limit: Increasing the WordPress Memory Limit. It's recommended to have at least 128mb.
2) Make sure you have at least PHP 5.6 installed. You can check that in WooCommerce > System status.
3) Make sure you have at least WordPress 4.5 installed.
If that does not work there is probably a plugin conflict. Try this:
1) Disable all plugin.
2) Check if you still can't open the Customizer or UX Builder.
3) If it works try add activate the plugins again one by one and test.