I see the same behaviour. And that behaviour could change after removing and installing the app again. The device versions and OS versions varies. There is no structure there. We now have about 500 voip calls a day and about 20% of these are failing bacause the push notification could not be handled. That's way too much!
Edwin.vermeer
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We see a similar pattern. We have about 500 voip calls a day and for 20% the push notification are not picked up by our app. When doing some tests ourself the behaviour varies. Indeed it's often the case that the app is suspended/killed and the screen is off, but often the push notification will arive in that situation. We also see that VOIP push notifications sometimes also not arive when the app is active. This last behavior will increase when you switch from WiFi to 3G or back.