Managed Backups returns Other kind of backup error

On a AWS/CentOS/WHM stack, Managed Backups keeps returning a "Other kind of backup error".
We tried increasing the memory to 512M and execution time to 300. Neither helped. We added the custom Snapshot Manged Backup defines to the wp-config.php.
That did not help either. Best we got was 50% before Snapshot returned the error.