Unity reward video always stuck when Buffering

When buffering, unity reward video always stuck there and never continue to play, I have to quit the app, anyone encounter such problem? I am using Unity5.3.3P2, tested on IOS.

I re-import UnityAds.bundle and UnityAds.framework to the xcode project root, seems it works so far.

Edit: No, still stuck there sometimes and could not get a error callback to exit.