This notice isn’t helpful. On the same page there is something like:
Revisions: 29 Browse
After you have clicked Restore the backup, you can click on Browse. This will take you to the revisions of the page. If you move the slider all the way to the right, it will display an [Autosave] revision. You can click Restore This Revision to recover the autosave version.
Note: I can’t confirm nor deny this, but it could be an Avada theme issue.