On a SharePoint 2013 intranet, I created a discussion with "Created By" being one of the column.
The column is to show the Office, users are from. The office is displayed for some users while being blank for others. If I change the field to show name instead of office, it will show the name for every user.
I looked at their profiles on the SharePoint Server and the Office field has data. The same thing happens on another discussion board with the same field and users.