@JustinMicheal-7973
We have created around 20,000 MailUser objects, but have only migrated 9. We have 50 scheduled for next week and noticed these 2 “missing”
Azure AD changes were taking hours to replicate to ExO
Based your description, although AAD Connect sync is unstable, it still works. I guess this phenomenon caused by this account broken or there exist sync issue between your AAD and Exchange online:
About the account broken issue, you could try to delete this MailUser from Exchange on-premise, then try to recreate a new one, check whether this new on could show in Exchange online after syncing.
About the sync issue, you could open a service request from Microsoft 365 admin center to let Microsoft to help you check from the backend.
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