Check if mopub banner ad is on screen

I'm doing an iOS game. if banner loads I need to pull my UI a bit up. I'm using mopub sdk in my xCode project. I'm listening to these methods in xCode:

 adDidFinishLoadingAd -> move UI up;
 adDidFailToLoadAd -> move UI down;
 adDidClose -> move UI down;
 adActionDidFinish -> move UI down;

but sometimes the ad disappears without calling any of these methods and keeps the UI up. any way to check if the ad is visible at the moment?

thank you