I just ran across the same issue. Manually running the backup (even with the service account) was running fine but the scheduled task was not working with the same result as you got.
After creating the scheduled task with "Backup and Verify" instead of the "Backup Wizard" the job was running fine which made me confused. So I checked the details of the job and it turned out that the option "-RetainUtmBackups" must not be 0. And since you set "-BackupTruncatedLogs" to false SME will not backup the logs to be truncated anyways, so the option "-RetainUtmBackups" is somewhat redundant.
Try to change it to 1 instead of 0 and the scheduled task should run without issues.
You'll also see when you use "Backup and Verify" in the SME console instead of the "Backup Wizard" that you cannot choose "0" in the "Up-to-the-minute Restore Options" (where as in the Backup Wizard you can specify 0). So I assume this is a bug in the GUI.