Hi Leanne,
To make this clear, the update you did on the staging site went well, right? I don’t see the big gap underneath the logo carousel anymore.
So the issue now is you can not migrate your staging update to the live site.
Would you mind to provide a walkthrough on that Sync back process? The error you show seems to be pointing (not directly) that your process is just overwriting the old folders/files and not deleting it first before copying the updated files. If you do not have control over this process please contact your hosting to assist you on this.
But since you have already the backup and the update went well on the staging, I advise that you do the update now directly on the live site. Since you can’t do the automatic update because your X and Cornerstone is outdated, Please follow the Manual X Update Via FTP guide provided here.
After you successfully update the X, deactivate and delete your old Cornerstone, then navigate to X > Validation, wait for a few seconds and X will automatically re-install the Cornerstone that is compatible to it.
After the successful re-installing of Cornerstone, validated your live site, so you can update the Extensions (Rev Slider, X – Under Construction, and other 3 party plugins).
Remember to clear all caches (plugin, server-side, CDN, and browser’s cache) after updating so that the code from the latest release is always in use. This will help you to avoid any potential errors.
Let us know how it goes,
Cheers!