UnityAds video is not paused on iOS when multitasking

Hi,
I am using Unity 5.3.6, I use Unity Ads through the editor->windows->service->UnityAds. The ads works on Android device when I multitasking it can be paused automatically, however, it is not paused on iOS (ads continue playing if I double press home button and it goes to the multitasking small window, or the ads skip if I press home button once and the game goes to the background). Do anybody have ideas on how to make it paused on iOS when multitasking?

Thanks!