Rewarded ad shows static interstitals...

Zwire

and when static interstitial should appear, a rewarded ad turns op. This seems to not always happen but 1/3 of the time.

I experienced this with my published game on android.

Why doesnt the rewarded ad show a rewarded video 100% of the time but often a static interstitial?

@adent42 - you know how to fix this or anybody else?