I installed iOS 9 GM a week ago (clean install) and I've been having this issue with some notifications not consistently notifying with a sound or vibration. For example, the gmail app will alert with the sound/vibration about 80% of the time and 20% of the time the notification will just light up on my screen without vibrating/sounding off. After playing around with some of my apps, I realized it has to do with those apps that use stock tones (like tri-tone) and those that use their custom sounds. if the app uses a stock iOS tone it will always notify with a vibration or sound. if it has a custom sound, it exhibits that ~80% rule. I've updated today to the iOS 9 release version and still experiencing the same thing. Anyone else getting the same issue? Thanks in advance.