Did you import the business area that the folder belongs in as well? If not, it will not be assigned.
It is probably imported but was imported as an orphan and you should be able to see it if you use File | Manage Folders.
My advice would be to export the business area that it belongs to then re-import. During the import check the box to Refresh objects that already exist.
Hope this helps
I got the DBA team to create the folder in the environments then migrations worked fine.