Pease check for the following first:
- We'd recommend that you increase your memory allocated to PHP if you haven't done so already. 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 the issue is still there, please make sure that you have everything updated to the latest version especially for X and Cornerstone. You can find more info about the support versions of X and its bundled plugins here.
If you are still seeing an issue, please 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.
Let us know how it goes!