Hey @graemed1378,
Thanks for writing in! Did you revert back to the previous version? I am seeing X (9.0.8) and Cornerstone (6.0.8) were currently installed when I checked your site.
One thing to keep in mind is that After doing the updates, always remember to clear all caches especially because you have installed the WP Fastest Cache plugin so that the code from the latest release is always in use. This will help you to avoid any potential errors.
And please clear your browser cache too. You may use private browsing mode in testing your site to make sure that you are viewing the latest codes from the updates and not the cached version in your browser.
If the error exists, we recommend that you clone your live site to a staging site. The staging site is very useful because you can test drive any X updates in the staging area, do the customizations and troubleshooting without disrupting your live site. Once everything is perfect, you can easily and flawlessly proceed with the update on the live site. To know how to create a staging area, please check out these articles:
Kindly let us know how it goes.