Not booting up from SD Backup

[Gusto5]

When I try to boot from a SD backup, shown in the startup disc options, even though I selected the Backup as the startup disc, my MBP will only boot from the internal SSD and not the backup. Both the internal (Mac HD) and external (MBP Backup) SSDs appear during the startup options. Why wont my MBP allow me to boot from the SD backup?
I'm running Sonoma 14.6.1 with SuperDuper 3.9.1 (V134)

[davebarnes]

I also have this problem.
New SSD from OWC.
Partitioned into volumes:
Bootable Backup
Time Machine Backup

Ran SuperDuper! with erase and backup.
Have Container 3 with Bootable Backup and Bootable Backup - Data underneath it.

Restart iMac with option key.
See both internal drive and Bootable Backup
Select Bootable Backup and the boot process starts and then I get an error message and it reboots using the internal drive.

The only difference I can see is that the old Bootable_Backup owner is Root (0) and my new Bootable Backup owner is Dave (503)

[dnanian]

Please try v3.10, the current version. Make a complete erase-then-copy backup with that before attempting to boot.