It's stored as a reference rather than the name itself, WFA looks up the other attributes. Are your root_volume_id's empty in your database?
Try a query like this in MySQL Workbench or similar to match root volumes and qtree ID's with either objects, and see if they populate or you get NULL's.
SELECT vfiler.name, vfiler.root_volume_id, (SELECT volume.name
FROM storage.vfiler as vfiler2,storage.volume
WHERE volume.id = vfiler2.root_volume_id and vfiler.id = vfiler2.id) as volume_name,
vfiler.root_qtree_id, (SELECT qtree.name
FROM storage.vfiler as vfiler2,storage.qtree
WHERE qtree.id = vfiler2.root_qtree_id and vfiler.id = vfiler2.id) as qtree_name
For me, the root_qtree_id's are all empty, but the root_volume_id's are ok, and the command will automatically adjust in this case (and assume they are in /vol/<root-vol>/etc/quotas).
There may be a collection issue, where root_volume information is not being gather.
If the fields don't exist in the wfa database, was there an upgrade involved? You could try to "Reset Schema" and kick off a collection and see if they re-appear..