Users may be unable to join Microsoft Teams meetings and see sign-in errors

Timeline (UK time)

1. 16 Oct 2026, 05:33 BST ✓ Operational

   Title: Users may be unable to join Microsoft Teams meetings and see sign-in errors User impact: Users may have been unable to join Microsoft Teams meetings and saw sign-in errors. More info: Affected users saw a sign-in prompt when they attempted to join a meeting but clicking "sign-in" on the prompt had no effect. Users can sign-out and sign back in as a temporary mitigation. Final status: We've completed the deployment of our code fix to all affected environments and confirmed through telemetry, along with a subset of impacted users, that the issue is resolved. Scope of impact: Some users who attempted to join Microsoft Teams meetings may have been affected by this issue. Start time: Wednesday, October 7, 2026, at 1:00 AM UTC End time: Friday, October 16, 2026, at 3:30 AM UTC Root cause: A recent change to the authentication flow utilized in the event contained a regression, which resulted in impact. Next steps: - We're reviewing our feature update testing and validation methods to better identify the potential for impact to the Microsoft Teams meetings and sign-in authentication path prior to deployment to prevent similar impact in the future, and to improve our pre-deployment update testing processes. This is the final update for the event.

2. 16 Oct 2026, 01:35 BST ✓ Operational

   Title: Users may be unable to join Microsoft Teams meetings and see sign-in errors User impact: Users may be unable to join Microsoft Teams meetings and see sign-in errors. More info: Affected users see a sign-in prompt when attempting to join a meeting but clicking "sign-in" on the prompt has no effect. Users can sign-out and sign back in as a temporary mitigation. Current status: Our code fix has nearly completed propagation throughout most of the affected environments and we're continuing to monitor it as it progresses. We anticipate it'll have fully propagated by our next scheduled communications update. Scope of impact: Some users attempting to join Microsoft Teams meetings may be affected by this issue. This information may be updated as our investigation continues. Start time: Wednesday, October 7, 2026, at 1:00 AM UTC Root cause: A recent change to the authentication flow utilized in the event contained a regression, resulting in this impact. Next update by: Friday, October 16, 2026, at 5:30 AM UTC

3. 14 Oct 2026, 22:49 BST ✓ Operational

   Title: Users may be unable to join Microsoft Teams meetings and see sign-in errors User impact: Users may be unable to join Microsoft Teams meetings and see sign-in errors. More info: Affected users see a sign-in prompt when attempting to join a meeting but clicking "sign-in" on the prompt has no effect. Users can sign-out and sign back in as a temporary mitigation. Current status: We've halted the code change causing this problem to ensure that no additional users encounter Microsoft Teams meeting join and sign-in errors. We're deploying a code fix to remediate the issue for users who received the code change prior to us halting it. Users will experience progressive relief from the issue as this deployment reaches them and we expect the code fix to propagate fully around the time of our next update. Scope of impact: Some users may be unable to join Microsoft Teams meetings and see sign-in errors. This information may be updated as our investigation continues. Start time: Wednesday, October 7, 2026, at 1:00 AM UTC Root cause: A recent change to the authentication flow utilized in the event contained a regression, resulting in this impact. Next update by: Thursday, October 15, 2026, at 11:30 PM UTC

4. 14 Oct 2026, 03:06 BST ✓ Operational

   Title: Some users may be unable to join Microsoft Teams meetings and see sign-in errors User impact: Users may be unable to join Microsoft Teams meetings and see sign-in errors. More info: Affected users see a sign-in prompt when attempting to join a meeting but clicking "sign-in" on the prompt has no effect. Users can sign-out and sign back in as a temporary mitigation. Current status: We’re monitoring the rollback of the offending change and expect that a remediation timeline will be provided by our next scheduled communications update. Scope of impact: Some users may be unable to join Microsoft Teams meetings and see sign-in errors. This information may be updated as our investigation continues. Start time: Wednesday, October 7, 2026, at 1:00 AM UTC Root cause: A recent change to the authentication flow utilized in the event contained a regression, resulting in this impact. Next update by: Wednesday, October 14, 2026, at 10:00 PM UTC

5. 14 Oct 2026, 00:51 BST ✓ Operational

   Title: Some users may be unable to join Microsoft Teams meetings and see sign-in errors User impact: Users may be unable to join Microsoft Teams meetings and see sign-in errors. More info: Affected users see a sign-in prompt when attempting to join a meeting but clicking "sign-in" on the prompt has no effect. Users can sign-out and sign back in as a temporary mitigation. Current status: We've initiated our rollback of the responsible change and will monitor this rollback to provide a mitigation timeline as it becomes available. Scope of impact: Some users may be unable to join Microsoft Teams meetings and see sign-in errors. This information may be updated as our investigation continues. Start time: Wednesday, October 7, 2026, at 1:00 AM UTC Root cause: A recent change to the authentication flow utilized in the event contained a regression, resulting in this impact. Next update by: Wednesday, October 14, 2026, at 3:30 AM UTC

6. 13 Oct 2026, 23:00 BST ✓ Operational

   Title: Some users may be unable to join Microsoft Teams meetings and see sign-in errors User impact: Users may be unable to join Microsoft Teams meetings and see sign-in errors. More info: Affected users see a sign-in prompt when attempting to join a meeting but clicking "sign-in" on the prompt has no effect. Users can sign-out and sign back in as a temporary mitigation. Current status: We've confirmed a recent change to the authentication flow utilized in the event contained a regression, resulting in this impact. We're preparing to rollback this change in the affected environments and will provide a remediation timeline as soon as one becomes available. Scope of impact: Some users may be unable to join Microsoft Teams meetings and see sign-in errors. This information may be updated as our investigation continues. Start time: Wednesday, October 7, 2026, at 1:00 AM UTC Root cause: A recent change to the authentication flow utilized in the event contained a regression, resulting in this impact. Next update by: Wednesday, October 14, 2026, at 12:00 AM UTC

7. 13 Oct 2026, 19:56 BST ✓ Operational

   Title: Some users may be unable to join Microsoft Teams meetings and see sign-in errors User impact: Users may be unable to join Microsoft Teams meetings and see sign-in errors. More info: Affected users see a sign-in prompt when attempting to join a meeting but clicking "sign-in" on the prompt has no effect. Users can sign-out and sign back in as a temporary mitigation. Current status: We're continuing to review the logs provided by a subset of affected users alongside service side data in order to develop the most effective remediation steps. Scope of impact: Some users may be unable to join Microsoft Teams meetings and see sign-in errors. This information may be updated as our investigation continues. Next update by: Tuesday, October 13, 2026, at 10:00 PM UTC

8. 13 Oct 2026, 18:18 BST ✓ Operational

   Title: Some users may be unable to join Microsoft Teams meetings and see sign-in errors User impact: Users may be unable to join Microsoft Teams meetings and see sign-in errors. More info: Affected users see a sign-in prompt when attempting to join a meeting but clicking "sign-in" on the prompt has no effect. Users can sign-out and sign back in as a temporary mitigation. Current status: We're reviewing the logs provided by a subset of affected users and have requested an additional set of fresh logs from those users to assist in pinpointing the underlying root cause of this event, so we may develop the most effective remediation steps. Scope of impact: Some users may be unable to join Microsoft Teams meetings and see sign-in errors. This information may be updated as our investigation continues. Next update by: Tuesday, October 13, 2026, at 7:00 PM UTC

9. 13 Oct 2026, 17:57 BST ✓ Operational

   Title: Some users may be unable to join Microsoft Teams meetings and see sign-in errors User impact: Users may be unable to join Microsoft Teams meetings and see sign-in errors. More info: Affected users see a sign-in prompt when attempting to join a meeting but clicking "sign-in" on the prompt has no effect. Users can sign-out and sign back in as a temporary mitigation. Current status: We're investigating a potential issue with Microsoft Teams and checking for impact to your organization. We'll provide an update within 30 minutes.