I've checked your website and I can see you are using an old version of X theme (version 5.2.5) along with the latest version of Cornerstone plugin. This might cause the problem you are having here. I recommend updating X theme to the latest stable version following this guide:
Then you can clear cache on your website and recheck this issue. If this didn't help, then please send us your WordPress Dashboard login details in a "Secure Note" so we can investigate this issue.