I use iAd interstitials in my game every third death, but most of the time it doesn't show up. I was thinking that maybe it's because they run out of ads to show so I might need to have multiple ad companies within my game, but I don't know for sure. If anyone knows I'd really appreciate it! Thank you!
iAd will close 30.06.2016 I no longer reckon here with good ad rates. Everybody will switch to other ad networks.