Microsoft 365 Alert – Service Degradation – Microsoft Defender XDR – Some users with Conditional Access App Control may be experiencing sign-in failures in Microsoft Defender XDR – RESOLVED

02/09/2026 09:51:00 AM

NHS.net Connect Reference: INC46923947

Microsoft Reference: DZ1465561

Issue Status: RESOLVED

Issue Description: Users with Conditional Access App Control may have experienced sign-in failures in Microsoft Defender XDR.

Current Update: 02/09/2026 09:52:00 AM – Microsoft has validated with impacted users and their internal monitoring telemetry that all traffic is being served by healthy services and impact is remediated.

Scope of impact: Your organisation was affected by this event, and some users with Conditional Access App Control experiencing sign-in failures in Microsoft Defender XDR may have been impacted.

Root cause: A network authentication component misconfiguration affecting authentication for protected applications was preventing some regional service instances from retrieving the organisational sign-in configurations required to process requests.

Next steps: Microsoft is reviewing and improving our validation process for network authentication component configuration changes to prevent similar issue from occurring in the future.