I suspect this could be a cache issue, please make sure to clear all your cache features associated with your website. Please also go to Cornerstone > Settings > System and hit the “Clear Style Cache”, this should clear the Cornerstone cache.
Only if none of that helps, please give us the following information in a Secure Note.
WordPress Login URL
Admin level username and password
You can find the Secure Note button at the bottom of your posts.
It seems that it might be the issue of version compatibility issue. Please make sure your WordPress version is updated and the PHP version is 7.4 or 7.4+ as per our version compatibility page.
It is also recommended by WordPress as well please have a look at this article.
I would suggest you please purge all the cache from the server-side. I would suggest you troubleshoot with a few of the common issues before we investigate your settings.
If it doesn’t work, I would suggest you follow these steps.
Activate the default theme of WordPress and deactivate the X theme
Delete the X theme and Cornerstone plugin
Download the fresh copy of the X theme from the Themeco account dashboard
Reinstall the X theme, after the X theme is installed, use the link in the dashboard to automatically install the Cornerstone.
Please note you must have the backup of the site database and files before performing the above steps.
If none of those work, It would be best if you could copy your live website to your staging area. and send your details in a secure note so that we can investigate your setting without breaking your live site. Please provide the following details
WordPress Login URL
Admin level username and password
FTP Details
You can find the Secure Note button at the bottom of your posts