We are experiencing the following problem using GeoAnalytics within Qlik Sense.
Trying to do a drill down on a Qlik Sense GeoAnalytics map and area object, and putting a drill down dimension based on 2 fileds (State->County), the map doesn’t show what expected:
As a solution, we decided to add a field in the data model (County & ' county, '&State&', US' AS COUNTY2).
In this way, both the table and the map shows the expected counties only.
You can find an attached qvf file that shows this problem.
There is nothing wrong with your solution. And, you don't need to create that field in the script,it all can be done on the front end in the properties of the layers. See this video, after 5 min: