Hi!
Thanks for taking the time to reach out to us. To better help you can you confirm my understanding of the issue you are facing.
When logged into your site and viewing a page you click on “Customize” from the wordpress admin bar. When the Customizer opens it is showing you nothing in the right panel when you would expect to see your site.
Is this correct?
Also can you please verify for me that you verified this issue was occurring even when using the Twenty Eleven theme with only The Events Calendar and Events Calendar PRO installed?
I ask in that I tested this setup on my local environment and am able to see the Live Preview from Customizer without issue.
Thanks for your assistance in getting this issue resolved,
– Matthew