Hi There,
Did the issue already resolve? Your X Theme is already up to date (https://prnt.sc/gsjyt0) and I was able to update the Cornerstone to the latest version without error (https://prnt.sc/gsjzto). Please clarify.
I advice to update your WordPress and outdated Plugins to the latest version to avoid any incompatibility issue.
Updating WordPress
Another thing, please update your X – Google Analytics extension to the latest supported version (refer here).
To update this extension to version 2.x, follow these steps:
-Ensure your theme is validated so Extensions can be installed automaticaly
-Deactivate and delete the plugin._
-On the theme overview page, locate and install the plugin from "Extensions".
-Visit "Plugins" in your Dashbaord to activate the newly installed version.
Because all of the plugin settings are stored in the database, and because version 2.x will migrate settings from older versions, it's safe to use this method of deleting the previous version.
Thanks,