A few days ago I upgraded to the new AdMob for mobile. I then proceeded to play around with mediation and suddenly my legacy publisher ID’s all stopped working. I’ve heard nothing from Google after submitting countless requests. By replacing the older publisher ID’s with the new one’s my ads are appearing, but this does nothing for the users on the App Store. They will be broken until Apple approves the new version of You Doodle containing the new publisher ID.
In short, don’t mess with your new AdMob account settings until you have rolled out updates to your apps with the new publisher ID’s.
*UPDATE* It looks like somebody at Google got one of my emails. My ads are running again.