We found that the metadata columns which use the term store, end up showing empty for all users apart from the Site Administrators. To fix this you need to grant privileges to the users in this list.
To do this navigate to: http://intranet/Lists/TaxonomyHiddenList/AllItems.aspx
Click on “List”->”List Settings” then click on “Permissions for this list.”
Add permissions of the users you need to see the metadata, to the permissions list with read permissions, then try the list again, they should be able to see the metadata and therefore any columns that include that data don’t show empty or null.