If you experience problems with Push Notifications on iOS 9 (sometimes no sound): It is a bug in iOS 9. Apple will have to release an update. All iOS Apps have this problems from time to time on iOS9, also WhatsApp etc.. Please see e.g.: https://forums.developer.apple.com/thread/18395 and http://www.heise.de/newsticker/meldung/Probleme-in-iOS-9-Stumme-Benachrichtigungen-verfruehte-Display-Sperre-2837871.html