You need to resolve the Active Directory issue.
What should you do?
IdFix is used to perform discovery and remediation of identity objects and their attributes in an on-premises Active Directory environment in preparation for migration to Azure Active Directory. IdFix is intended for the Active Directory administrators responsible for directory synchronization with Azure Active Directory.
Scenario: Active Directory Issue
Several users in humongousinsurance.com have UPNs that contain special characters.
You suspect that some of the characters are unsupported in Azure AD.