Defender for Cloud MCSB enabled but assessments and Secure Score remain empty

Microsoft Defender for Cloud security-posture data is not being generated for a newly configured Azure lab subscription.

Configuration verified:

• Microsoft.Security and Microsoft.PolicyInsights providers are registered.
• Foundational CSPM is Standard.
• Microsoft Cloud Security Benchmark is ON.
• The SecurityCenterBuiltIn policy assignment exists with Default enforcement and references the Microsoft Cloud Security Benchmark policy initiative.
• A manual policy evaluation completed and current Azure Policy compliance states are available.
• Defender for Storage is Standard and functioning correctly.
• Defender for Storage sample alerts successfully trigger a high-severity workflow automation, Logic App and Microsoft Teams notification.

However:

• Azure Resource Graph returns zero Microsoft.Security/assessments records.
• az security secure-scores list returns no records.
• Requesting ascScore returns HTTP 404.
• Microsoft.Security/standardAssignments returns an empty list.
• A documented Audit standard-assignment PUT failed with HTTP 500: “Failed to validate standard assignment.”
• Azure Activity Log confirms “Create security standard assignments” failed with HTTP 500.
• Defender for Cloud Security posture does not load in the Azure portal.
• There are no active Azure Service Health incidents or health advisories.

This has persisted for more than 24 hours.

Is there a supported way to reinitialise Foundational CSPM/security-posture onboarding without disabling the working Defender for Storage plan or deleting the existing SecurityCenterBuiltIn policy assignment?

I can provide the timestamp and correlation ID privately if required.