Hello,
Thanks for reporting this, and sorry you faced such difficulty.
We looked into this and confirmed that each of your migrations had different prefixes, causing mail to be placed in different folders. We therefore did not have messages to compare against, since the prefixes were new folders. To ensure that duplicates are detected, please ensure that the prefixes of migrations are kept the same.
If you have any questions, please don't hesitate to contact us.
Sincerely,
The MoveMyMail Team