Thanks for writing in! If the URL is changed correctly, you should be able to validate your site. In case if you're not sure, please follow our migration guide here which explains how you should change your URLs.
If that is not the case, then you will need to follow our troubleshooting guide here.
If that doesn't help, you need to update your X theme and Cornerstone plugin manually for once by following this guide (https://theme.co/apex/forum/t/setup-updating-your-themes-and-plugins/62).
Hope that helps.