Hello There,
Thanks for updating in! When customizing PRO theme, you may go to Appearance > Customizer or XPro > Launch > Options. In the left side panel, you will have the theme option settings. In the right side pane is the preview. If you are only seeing a loading screens, there might be some JS error or conflict the prevents the site from loading in the preview area. You could try testing for a plugin conflict. You can do this by deactivating all third party plugins, and seeing if the problem remains. If it’s fixed, you’ll know a plugin caused the problem, and you can narrow down which one by reactivating them one at a time.
Sometimes, a loading screen means that you have exhausted your PHP memory limit. We recommend that you increase your memory allocated to PHP. To increase it, please edit your wp-config.php file and insert these lines:
define( 'WP_MEMORY_LIMIT', '256M' );
define( 'WP_MAX_MEMORY_LIMIT', '512M' );
If still nothing is working, would you mind providing us some WP access so that we can take a closer look?
Best Regards.