Microsoft reports that this is due to a duplicate SPN (Server Principle Name) While processing a change to the DNS Host Name for an object, the Service Principal Name values could not be kept in sync. The error number 8647 translates to symbolic name is ERROR_DS_SPN_VALUE_NOT_UNIQUE_IN_FOREST.
This was due to the object being already in the forest but out of the current scope of ODMAD. This issue will also happen during intra-forest migration because ODMAD does not delete the source AD object when performing Cutover.
To resolve the issue, please remove the Duplicate object from the target environment.
As for intra-forest migrations, there's currently no automated way to migrate machines. It's possible to modify a Cutover script, adding a custom task, that will delete a source AD machine account before joining to the target. Or do it manually.
Replication will need to be forced after deletion to make sure that original SPN will get cleaned properly prior to joining the target domain.
