Microsoft 365 Alert – Service Degradation – Exchange Online – Some users may be unable to access Microsoft 365 apps through the app launcher in Outlook on the web – RESOLVED

11/12/2025 08:56:00 AM

NHSmail Reference: INC46703259

Microsoft Reference: EX1193572

Issue Status: RESOLVED

Issue Description: Users may be unable to access Microsoft 365 apps through the app launcher in Outlook on the web.

Final Status: 23/12/2025 08:58:00 AM – Microsoft have confirmed that the deployment of the fix has completed, and they have validated with some users who initially reported the issue that the impact is remediated.

Scope of impact: Some users that attempted to access Microsoft 365 apps through the app launcher in Outlook on the web may have been impacted.

Root cause: A recent upgrade to .NET Core caused cache failures, which prevented users from accessing Microsoft 365 apps through the app launcher in Outlook on the web.

Next Steps: Microsoft are further reviewing the recent upgrade to understand what specifically caused the cache failures, and to understand what prevented it from being detected in our update testing and validation procedures, which will allow us to prevent similar issues in future upgrades.