I believe errors in non-interactive mode are still logged to /var/log/dist-upgrade/main.log (your failed attempt would be in /var/log/dist-upgrade/<date of failed attempt>/main.log.
I believe errors in non-interactive mode are still logged to /var/log/ dist-upgrade/ main.log (your failed attempt would be in /var/log/ dist-upgrade/ <date of failed attempt>/main.log.