backup of mysql failed

When performing a backup of any of my Virtual Server's and including MySQL I'm receiving the below failure. There are no details as to why it's failing though.

Starting backup of 1 domains to local file /backup .. Creating backup for virtual server .. .. backup of mysql failed : Backup failed! See the progress output above for the reason why.

• Backup under Webmin MySQL module works without issue
• Running via CLI with --debug gives no additional information
• Backups without MySQL create valid .tar.gz file owned by root
• Latest Webmin version as of this post and latest MySQL version (5.6)

I wasn't able to find anything else about why this might be happening, any help is appreciated.