Oh it's a kids game. Does your game comply with all 5 million family friendly requirements?
The highlights: support.google.com/admob/answer/6223431
Google is a pain when it comes to ads in kids games, that could be why it works fine in debug mode and not when downloaded from Google Play.
This is the way I test my games (over explained). I create an apk (NOT debug) and download that to my hard drive, then I upload it to my Gdrive so I can test it on several devices. Once on the Gdrive, I download it to every phone in the house - even the old ones.
I install it on each phone and test it, I especially look for when the ads pop up. Do NOT touch your own ads and do not use them to get stuff, but you can view your ads without ******* off the Google God.
If the apk (not debug) downloaded to your phone gives you real ads when played, but the bundle you uploaded to Google Play doesn't - Google is probably stopping it.
I played about 12 games in your app, but didn't get any ads. I went back to the menu screen several times.
Try the test I mentioned above to see if you get the ads. If you do, Google Play is probably stopping them for some reason.