可能有以下原因：
此时没有获取到 Ad -> The ad request was successful, but no ad was returned.
Note: New iOS apps will not show Google ads until they're listed in the Apple App Store. -> 用以前的 app id 来测试真实广告，或者配置成测试模式。 -> 看起来每个 app 必须在 AdMob 上新建独立的 app 单元
Have you followed all the instructions in the Google Developers Get Started guide?
Have you integrated the Google Mobile Ads SDK correctly?
Is your ad implementation code working properly?
Have you reviewed your error codes?
怎么解决：
换其他广告网络
试试 Banner
新建独立的 app 和 ad unit单元