Are you using X on the site? If so, please double check if you have both X and Cornerstone updated to the latest verrsion. Here is a link for a details information on how to do an update:
Please remember to clear all caches when updating so that the code from the latest release is always in use. This will help you to avoid any potential errors or any unexpected display issue on the site.
If both are updated, please try testing for a plugin conflict. 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.
In case the issue persists, please provide the link of the site in question so that we can check it.