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I wouldn't treat this as widespread unless Microsoft 365 service health shows an active Exchange Online advisory. To separate EAC trouble from RBAC or object scope, connect to Exchange Online PowerShell with the same account and run Get-DistributionGroup against an affected list.

If PowerShell also fails, confirm Exchange Administrator is active, especially with PIM, then sign out and back in to refresh the token. Distribution-list management normally requires Organization Management or Recipient Management in Exchange RBAC. Also check whether the list is directory-synchronized; synchronized lists must be changed in on-premises Exchange or Active Directory.

If only certain cloud lists fail, inspect ManagedBy. Some changes require the administrator to be an owner unless the admin cmdlet uses BypassSecurityGroupManagerCheck. If PowerShell succeeds while EAC fails, test a private browser session, capture the EAC correlation ID and UTC time, and open a Microsoft 365 support case.