AWS RDS MySQL restore stalling

When working with RDS, I would occasionally find my web console-initiated restores-from-s3 stall out indefinitely with no errors of any kind.  Confused, I ran to AWS Support, who told me that I should not specify "root" as the admin user when restoring the database to RDS.  This is because the backup already contains a root user, and it was causing the restore to silently fail.

Long story short: never use "root" as the admin user when restoring a MySQL backup to RDS.