I have implemented application:didReceiveRemoteNotification:fetchCompletionHandler:, which is necessary to run after receiving a push notification. I have also turned on "Background Fetch" and "Remote notifications" background modes. And my push notifications include the content-available flag, set to 1.
If my app is in the Active, Background or Suspended state, this function gets called appropriately and the app temporarily moves into the Inactive state. However, if my app has been purged from the Suspended state due to a low memory issue (i.e. the user has opened a number of other apps since launching my app, a fairly common occurrence), it moves into the Not Running state. At that point, it doesn't call the didReceiveRemoteNotifications function.
The documentation for this function states:
If you enabled the remote notifications background mode, the system launches your app (or wakes it from the suspended state) and puts it in the background state when a remote notification arrives. However, the system does not automatically launch your app if the user has force-quit it. In that situation, the user must relaunch your app or restart the device before the system attempts to launch your app automatically again.
The scenario where the user force quits the app and so the app doesn't call this function is acceptable. But what I'm seeing instead is if the system terminates the app for a fairly common reason, then this function doesn't get called.
I've also tried implementing application:didReceiveRemoteNotification:, the deprecated function, to see if that gets called when the app is in the Not Running state. It doesn't.
