Can you tell me one more thing, Robin? How you exit from your game? I ask because if we not overwrite the mobile Back button and press, game will "exit" (but still in the memory) and if we reactivate the game Admob banner ads will not show anymore.
I don't know this "bug" related to Stencyl or Admob extension but not good for revenue.
Btw, I overwrite Back button az use nme.Lib.exit(); code to exit the game, but in the last days I tried Chartboost extension which ignore Back button overwrite(if we want to close interstitial) and Admob banner is not shown if we return the game.