In repositories that were LF v7 or earlier, folders did not have a volume association.  This is possible because the volume is a Windows location for documents and a LF folder is just an entry in the LF DB (not a windows object).  The folder volume association was a feature that was added with the introduction of LF v8.  When the repository was upgraded, the old folders were not assigned volumes automatically, and the only way they get a volume assigned is if you manually assign it.  If you have the default volume set to Parent Volume and the Parent Volume is missing, for folders, it leaves the volume blank on the new folder.  To resolve this, you must find folders with no volume and assign it a default volume.  Once all folders have a volume assigned, new folders will have a volume assigned.