Example of the warning.
WARNING: [1213-31-61-00000000] Skip adding Acl 'LocalDomainAdmins <LocalDomainAdmins@domain.com>' to the delegate list.
In most scenarios, the following information will show after the warning: The Acl is type Contact which is not accepted by Exchange/Outlook.
This is expected because a contact objects cannot be added to the Access Control List in Active Directory.
There is no resolution for this warning other than converting the contact objects to User Security Objects via Merge Contacts and re-migrating the data.