This exception "No available DCs for domain, cannot process LDAP request for object" will occur when DirSync cannot locate the object based on the object DN in the specified Global Catalog Server. DirSync will search the object based on the DN via the specified DCs in the DC list.
The target contact object was deleted
Verify this users DN is correct. Additionally, reconnecting the tenant may help. This can be done from the 'Settings' gear icon - 'Environments' tab
Highlight the object and click the 'Reconnect' action hotspot.
Confirm in workflow logs if a target contact object was created previously by Power365, and if there was a previous attempt at migrating this account had been deleted from the target Active Directory.
If yes, restore the target contact, then the preparation, sync and cutover for the account should work correctly.