iAd Interstitials not showing consistently? And not at all on the simulator

iAd interstitials aren't showing up at all on the iPhone simulator, and they don't show up consistently on my iPhone. I've gone to the Developer settings, changed the fill rate to 100%, and turned on Unlimited Ad Presentation. No difference... an interstitial will generally show the first time it's supposed to, and then won't show again for anywhere from a few minutes to fifteen minutes. No idea what is causing the difference in time.

Also, there doesn't seem to be a way to track if the interstitial is going to show or not / if it actually showed or didn't. I realize there's an interstitial delegate, but it seems that isn't used anymore. The way I am calling my interstitial is using viewController.interstitialPresentationPolicy = ADInterstitialPresentationPolicy.Automatic

Thanks!

via Chebli Mohamed