This issue is usually caused by version incompatibility. I see you're using the latest version of Cornerstone but not X. Please update X to the latest version also. It's also recommended to follow the Best Practices in Updating Your Theme and Plugins.
If updating does not help, it could be cause by third party plugins or scripts. You could try testing for a plugin conflict next. 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.