My problem is the same or similar.
My problem is: banners and interstitials are not showing.
I am using the latest version of XDK and Scirra (beta) (downloaded it 1 or 2 days ago).
I am using the official (Scirra provided) admob plugin.
It used to work on before, on my other 2 Play Store games.
Something I have tried, without desired effect: downgraded "CLI" in Intel XDK from 5.x to 4.x.