Validtion Error "devices is invalid" seen after removing a device from Panorama

• Managed Firewall removed from Panorama.
• When attempting to commit the following error is returned.

Validation Error:
Shared -> pre-rulebase -> security -> rules -> <rule_name> -> target -> devices -> <removed S/N> '<removed S/N>' is not a valid reference
Shared -> pre-rulebase -> security -> rules -> <rule_name> -> target -> devices is invalid

• Panorama with managed Firewalls
• Supported PAN-OS
• Validation error

• Serial Number (S/N)  does not exist in a device group but S/N is still referenced in a security policy.
• Security Policy only displays S/N that reside in device groups.

1. Add S/N back to the Panorama.
2. Choose an existing device group.
3. Add S/N to a device group.
4. Navigate to the Security Rule that was called in the error.
5. Remove the S/N from the Security Rule's Targets.
6. Remove S/N from Device Group.
7. Delete Device.
8. Commit.