Game not pausing when interstitials are showing up on iOS but it works as expected on android

we implemented heyzap ad mediation in our game and in the iOS Build when the interstitials are showing up the game scene behind the ad is not pausing automatically whereas in android the game is pausing when the interstitials are playing.

Just wanted to know if i'm missing something here and has anyone faced the same issue ?

also, we're using unity 5.6.1 and xcode 9