You're referring to X -> Validation section right ? If you're not updated correctly you may see the old menu. However those demos should be there under standard Demos.
Can you try re-installing X theme and Cornerstone plugin, that should resolve your issue. Basically you can download the latest version of X theme from your Envato account and then delete your current X theme and Cornerstone plugin from your site. You current settings will be saved in the database, so that you can safely delete.
Then re-install X theme from Appearance -> Themes section and then it will automatically install Cornerstone plugin as well. Then try to generate your demo content under X -> Validation section.
If you're still having issues, provide us with your WordPress login credentials in a secure note to check your issue further.