The version of your X and Cornerstone is not compatible, your current X (v4.6.4) is behind.
Please update your X theme to the latest version. Also, update all the plugins and extensions that is bundle with X (refer here for the latest compatible versions)
Updating Your Themes and Plugins
Remember to clear all caches (plugin, server-side, CDN, and browser's cache) after updating so that the code from the latest release is always in use. This will help you to avoid any potential errors.
Let us know how it goes,