If you're using X then make sure you update both Cornerstone and X theme to the latest version. We've seen similar issues happened due to the incompatible versions being installed. You can find the latest version numbers here: (http://theme.co/changelog/) Then you can compare them to what's installed on your site.
If you find anything to be out of date, you can review our update guide.
Also don't forget to clear all caches (browser, plugin and CDN) this could be happening due to the cache as well.
Let us know how this goes!