To resolve the issue, do the following:
- Create a new Active Directory group that is named "ContentSubmitters" and then grant Admistrators and NetworkService full access to the group using the Security tab on the AD object. This is a dummy group and should be used as a placeholder only. You might want to add a description so that the group is not removed.
- Force or wait for Active Directory replication.
- Restart the following services:
- Microsoft Exchange Search
- Microsoft Exchange Search Host Controller
This worked a treat for me! Almost immediately the StalledDuetoCI changed to either CopyingMessages or InitalSeeding on the problem mailboxes. The migration continues!