Why are some articles missing the location information?

Does the user account running the reports have access to view the group in question? If not, the location will not appear.

I created the group, and I'm an admin, so I would assume I have the required permissions.   

How did you make the group not navigable? Do you just mean it's created as a private unlisted group?

The group is joinless and active.  I just removed it from the menu bars, so the only way people can access it is by having the direct link.  

Are there any exceptions in the Exception Log or errors in the ETL log?

There are 3 errors - Socket Message Bus Service Unavailable (EC2AMAZ-PLDU4IJ to bus-001.prd1.telligent.use1:9681)

and 2 search index errors.  I'm not sure where to find the ETL log.

I added the group to the menu navigation last night and I can now see the location in the report.  I can also filter by that group, which I wasn't able to do before.  Strange that it would work this way, but good to know that a group has to be in the navigation somewhere to report on the articles.