1. Decrypt all the items in the Private Folder and migrate again.
2. If you migrate, using the option MigrateOrphanedDocs, it will migrate all of the content
from the private folders, it just will not be in the private folders.
It will be in the "All Documents" folder. and this might not be a viable option.
An enhancement request has been to add a "PrivateFoldersOnly" option
in next release of MNE TFS#652503