Thanks for writing in! First of all, could you please try testing for a plugin conflict by deactivating all of your third party plugins and see 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.
If you're still having issues, please try to have the PHP memory limit of your site increased.
To do this, please edit your wp-config.php file and insert these lines:
define( 'WP_MEMORY_LIMIT', '256M' );
define( 'WP_MAX_MEMORY_LIMIT', '512M' );
You can add it before the line
/*That's all, stop editing! Happy Blogging. */
Here is a details article about the PHP Memory Limit that is in our Knowledge Base (https://theme.co/apex/forum/t/troubleshooting-increasing-php-memory-limit/16935).
Also please go through our knowledge base article on how to troubleshooting builder loading issues (https://theme.co/apex/forum/t/troubleshooting-builder-preview-warnings/14404).
If you're still having issues, please provide us with your WordPress login credentials in a secure note to check your issue further.
Let us know how it goes.