Admins may see the incorrect user added to a group in the Exchange admin center when users have the same DisplayName

Title: Admins may see the incorrect user added to a group in the Exchange admin center when users have the same DisplayName
User impact: Admins may have seen the incorrect user added to a group in the Exchange admin center.
More info: This also affected admins or users who were group owners, and they may have received “failed to update member” error when attempting to add users to a group in the Exchange admin center.
Affected users may have also been unable to add members to Distribution Lists (DLs) that they owned using any Exchange Online connection method, such as the Outlook desktop app, Outlook on the web, and Outlook mobile apps. Admins could have reportedly utilized PowerShell to successfully add users to DLs.
Final status: We’ve completed deploying the fix to all impacted environments, and received confirmation from some admins who initially reported the issue that the fix successfully remediated the impact.
Scope of impact: Any admin or group owner that attempted to add users to a group in the Exchange admin center may have been impacted.
Start time: Monday, October 2, 2023, at 12:30 PM UTC
End time: Wednesday, October 18, 2023, at 8:30 AM UTC
Root cause: A recent update to the Exchange admin center was configured so that the Name property was used when adding members to a group and caused a conflict with the property matching another user’s DisplayName, which resulted in impact.
Next steps:
– We’re further reviewing the recent update to understand how the configuration conflict was introduced, 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 updates.
This is the final update for the event.