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 (256MB is even better).
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.