My site was running 12.1.0 and I ran a full backup before running the upgrade to 13.0.0 (from the Dashboard). The upgrade did not appear to complete after an hour+, and presented the error, "Site is temporarily unavailable due to scheduled maintenance, please try again in a minute." So I restored it from the backup I had made less than an hour before that, but the site is still presenting the same error. It is running Cron every five minutes. I cleared the cache in one of my browsers and still get the error. I can not get to Studio or any other part of the site.