Hi @dwsc,
Sorry for the delayed response. Did you continue using 3.5 or did you roll back to 3.4 after that happened? And do you have a backup of your database from before the upgrade? Unfortunately since your file settings were misconfigured when you first ran 3.5, it removed the old references to the files from your posts and failed to add the new ones to the FileInfo table. Your files still exist on S3, but Mattermost doesn't know about them any more.