Cannot delete Recovery Services vault - orphaned MARS FileFolder items (Unsupported WorkloadType)

I need to permanently delete a Recovery Services vault "Praxisserver" (Resource Group: Heimsicherung, Region: West Europe, but cannot remove the backup items that block deletion.

The vault contains 4 orphaned MARS (Azure Backup Agent) FileFolder items on 2 containers:

All items show ProtectionState=Protected, DeleteState=NotDeleted.

Every self-service method fails:

• Disable-AzRecoveryServicesBackupProtection -Item $it -RemoveRecoveryPoints returns "Unsupported WorkloadType: FileFolder"
• Unregister-AzRecoveryServicesBackupContainer returns BadRequest (items still protected)
• REST API DELETE on the protected item returns BMSUserErrorProtectedItemNameIncorrectFormat
• Disabling soft delete fails with BMSUserErrorDisablingSoftDeleteStateNotAllowed (secure-by-default region, West Europe)
• The official "delete vault" PowerShell script from the portal fails at the MARS unregister step, then vault deletion returns BMSUserErrorVaultDeletionNotAllowed

Root cause: the MARS agent on laackdent1 was re-registered to a different, currently active vault ("Praxis-Backup-LRS"). Therefore the MARS console on the server can no longer manage/stop these orphaned items in the old "Praxisserver" vault.

How can I remove these orphaned MARS FileFolder items so the vault can be deleted? The data is obsolete and can be permanently deleted. If this requires a server-side action by Microsoft, please advise on escalation.

Support plan: Developer.