My admob test ads show but real ads do not show. So I can see them on my phone and tablet which I have classified as "test devices" with Google but my Admob account is about to be banned because no ads are being shown. So apparently my app does not show ads on other devices. I only have about 700 users but one of them should have stayed long enough to trigger an add in the past couple of months.
The only thing I do not know how to check is the SDK that you upload to the gradle. I do not use Android Studio (I have for testing but not for anything else) but nothing about this is mentioned in FF documentation so I assume you are already using the correct SDK. I checked all the documentation, I don't know why they do not show.
Is there something that I am missing.