iOS 9: Playback pauses after device lock (if display inactive)

Hi, I'm using AUGraph to playback audio and found the strange issue like pause after device lock (plus works fine in background and after lock if display active)

and of course I set up the state and category for audio session:

[[AVAudioSession sharedInstance] setActive:YES error:&activationError];

[[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayback error:&setCategoryError];

and add background mode to the Info.plist

<key>UIBackgroundModes</key>

<array>

<string>audio</string>

</array>

Can anyone check? (It's my mistake or just a bug inside iOS 9)

Thanks