Views Table Grouping not working if group field is blank
I had a similar issue. If the field I was grouping by was empty in all the nodes under another grouping, no results would show. In my case it was State->Administrative Area, and if none of the nodes in the state had administrative areas no results would show under the state.

The solution that ended up working for me was to uncheck the 'Hide rewriting if empty' box in the Configure field: Content: Administrative Area->No Results Behavior section. 'Hide if empty' was already unchecked so I didn't fool about with it.