title: didActivateAudioSession is very rarely not called
body: <p>I am working on a CallKit enabled VOIP application and sometimes our clients are facing a problem that the <strong>didActivateAudioSession</strong> callback is never called by the iOS system. <br/><br/>
  Is there a known bug as this or do you think that we have something missing like setting the correct mode of the AVAudioSession or something like that?
  <br/><br/>
  This is how I prepare AVAudioSession before reporting call to the system by CallKit;</p>
  
  <pre><code>        AVAudioSession *audioSession = [AVAudioSession sharedInstance];
          [audioSession setCategory:AVAudioSessionCategoryPlayAndRecord withOptions:AVAudioSessionCategoryOptionAllowBluetooth error:nil];
          [audioSession setActive:YES error:nil];
  </code></pre>