The version of Wordpress you have is behind 4.8.3, the latest is 4.9.7, since this is a live site I advise that you restore the site from before this issue happened.
Then duplicate the site on a staging server, and do the updating there first (WP, Theme, Cornerstone, & Plugins) this way we can address the issue that might occur and address it, before you applied the update on the live site.
- How to duplicate a WordPress Site
- Updating WordPress
- Updating Your Themes and Plugins
- Latest Version Compatibility
If you have any caching and/or optimizer feature (plugin, server-side, CDN) on your site, please clear and deactivate those for now.
Let us know how it goes,