The migration for particular users is not starting and are being rescheduled. The following can be seen in the On Demand Migration for Email (ODME) migration log file:
Warning None Error detected, attempting retry 1 of 5 Active Directory is unavailable. Try again later. (Active Directory is unavail able. Try again later.)
Warning Mailbox Rescheduled Active Directory is unavailable.
Information Mailbox status Active Directory is unavailable.. This mailbox was rescheduled to run after 12/14/2018 11:13:21 PM UTC.
This is typically found to be a transient error in the Office 365 tenant and its Azure Active Directory. Typically, this error resolves itself in a few hours. If not, you may want to create a Service Request with Microsoft Support.
ODME will continue to retry the migration until it succeeds.
You can use the Microsoft Connectivity Analyzer, as described in this KB Article: How To: Test ODME migration admin account configuration using the Microsoft Connectivity Analyzer, when Test Connection fails in ODME to test connectivity.