However, you cannot migrate a Catalog that has been migrated already. So, you may have to duplicate it, deleted all cloud data (or at least the migrated data) and re-migrate.
It's best to get further advice on this though.
I don't know what happens if you re-migrate and leave the previous photos in the Cloud as I have never tried it. Ideally it would just create a Folder/Album structure and move the photos, although in reality, I assume it would create duplicates.