I develop locally with android-studio and a Galaxy S3 android phone connected via USB.
On my local development environment, when I fire up the run configuration to deploy on the S3, everything works fine - the map shows up just fine.
But when I deploy as signed APK to our server, and install via Internet (I am trying on another android phone to keep things clearly separated), the map tiles don't load, I see the Google sign to the lower left and the GPS location icon on the upper right corner.
I've seen a few related posts:
Android Google Maps application showing grey background instead of the map
which seems first a bit dated, second he uses eclipse (I am using android-studio), third - it didn't work for me.
Android - Google Maps Grey Screen on Signed APK This guy didn't get any useful answers to his question....