Hi Andi,
Thank you for writing in, is there an error showing up when you try to validate your site?
We just release X 7.1.1 and Cornerstone 4.1.1, please update to that version as that contains bug fixes (Changelog).
Updating Your Themes and Plugins
Remember to clear all your caching features (plugin, server-side, CDN, and browser’s cache) after updating so that the code from the latest release is always in use. This will help you to avoid any potential errors.
If the issue persists, please do 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.
Let us know how it goes,
Cheers!