Why do the Lock Screen audio controls disappear when I pause AVAudioPlayer?

You're on the right track ...

You seem to be missing setting;

  MPNowPlayingInfoCenter nowPlayingInfo

Without it, you will get the results described, IE after pressing pause, the lock screen no longer shows the pause, or indeed that it is playing a song. Here's a guide on how to set it (i've taken this from working code I did some time back, but I'm sure you can figure out what's what).

    MPMediaItemArtwork *artwork = [[MPMediaItemArtwork alloc]initWithImage:albumImage];    [MPNowPlayingInfoCenter defaultCenter].nowPlayingInfo = [NSDictionary dictionaryWithObjectsAndKeys:aSong.songTitle, MPMediaItemPropertyTitle,                                                             aSong.artistName, MPMediaItemPropertyArtist, artwork, MPMediaItemPropertyArtwork,  1.0f, MPNowPlayingInfoPropertyPlaybackRate, nil];

Add this Code in ViewDidLoad() For background play. It work for me. You should try it

    UIApplication.sharedApplication().beginReceivingRemoteControlEvents()    let session:AVAudioSession = AVAudioSession.sharedInstance()    do    {        try session.setCategory(AVAudioSessionCategoryPlayback)    }    catch    {        print("Background Play Error")    }