Thanks for writing in! Are you experiencing this error only on Chrome? If so, try clearing Chrome browser cache and then try to load and edit your site using Cornerstone.
If you're still having issues, you need to enable WP_DEBUG mode (https://codex.wordpress.org/WP_DEBUG) and then edit one your pages and see if you're getting any error messages.
If you're using a caching plugin, make sure to purge your server cache before testing.
Let us know how it goes.