激励广告的adDidDismissFullScreenContent回调未触发问题咨询

我遇到了iOS平台下Google AdMob激励广告的adDidDismissFullScreenContent回调无法触发的问题，该问题与AdMob开发者社区中描述的情况一致。

我同时使用presentInterstitialAd(fromRootViewController:)和presentRewardedAd(fromRootViewController:)方法分别展示插屏广告和激励广告。根据官方定义，GADFullScreenContentDelegate的以下代理方法应该对两种广告类型都生效：

// MARK: - GADFullScreenContentDelegate Methods
public func ad(_ ad: GADFullScreenPresentingAd, didFailToPresentFullScreenContentWithError error: Error)
{
    print("Ad did fail to present full screen content with error: \(error.localizedDescription)")
}

public func adWillPresentFullScreenContent(_ ad: GADFullScreenPresentingAd)
{
    print("Ad will present full screen content.")
}

public func adDidDismissFullScreenContent(_ ad: GADFullScreenPresentingAd) 
{
    print("Ad did dismiss full screen content.")
} 

但实际运行后发现，插屏广告的所有回调均正常触发，唯独激励广告展示完毕后，adDidDismissFullScreenContent回调完全没有被调用。

内容的提问来源于stack exchange，提问作者Mr.Schtelbe