This morning I just happened to be next to my server when it suddenly powered down. Concurrently I received the following email notice:
/bin/sh: line 1: 4681 Terminated /usr/local/emhttp/plugins/ca.backup/scripts/backup.php &> /dev/null 2>&1
Server powered up OK on restart. It looks like the backup completed fine, the last file creation being 6:55 am. The notification was 6.57 am the same time the server shut down. Am assuming there is a relationship.