Hello Ken,
Thanks for writing in! After doing the updates, always remember to clear all caches (if you are using WP Rocket, WP SuperCache or W3 Total Cache) when updating 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.
And also, before you update to the latest X Theme and Cornerstone plugin version, make sure that you are up to date with the latest versions:
This latest release contains fixes for several issues so be sure to check out the changelog:
We would highly recommend that you create 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:
Please let us know how it goes.