Microsoft 365 Alert – Service Degradation – Microsoft 365 Copilot Chat – Users may be unable to access Microsoft Copilot Chat in the browser and may encounter a 400 Request Header error – ONGOING

Announcements Shagufta Naaz

04/08/2026 08:54:00 AM

NHS.net Connect Reference: INC46899269

Microsoft Reference: CW1447067

Issue Status: ONGOING

Issue Description: Users may be unable to access Microsoft Copilot Chat in the browser and may encounter a 400 Request Header error.

More info: As a temporary workaround, some users may be able to mitigate the impact by clearing their browser cookies and then retrying access to Microsoft Copilot Chat.

Current Update: 04/08/2026 08:54:00 AM – Microsoft is reviewing service monitoring telemetry to isolate the source of the issue and establish a fix.

Scope of impact: Impact is specific to some users attempting to access Microsoft Copilot Chat in the browser.

Next update by: Tuesday, August 4, 2026, at 9:30 AM UTC