ios - iOS 9: オブザーバーを追加した後、AVPlayerViewController がコントロールを失った

Question

オブザーバーを追加した後、AVPlayer突然AVPlayerViewControllerコントロールを失いました。

-(void)viewDidAppear:(BOOL)animated {

    AVPlayerItem *playerItem = [[AVPlayerItem alloc]initWithURL:_playbackInfo.streamURL];

    // logo to show
    CGRect  viewRect = CGRectMake(10, 10, 30, 30);
    UIView *overlayView = [[UIView alloc] initWithFrame:viewRect];
    UIImageView *image = [[UIImageView alloc]initWithFrame:viewRect];
    image.image = _playbackInfo.logoType;
    [overlayView addSubview:image];

    self.player = [[AVPlayer alloc]initWithPlayerItem:playerItem];
    [self.contentOverlayView addSubview:overlayView];

    self.player.actionAtItemEnd = AVPlayerActionAtItemEndNone;

    [self.player addObserver:self
                  forKeyPath:@"rate"
                     options:NSKeyValueObservingOptionNew
                     context:NULL];


    [self.player play];
    [self.navigationController setNavigationBarHidden:YES animated:NO];
}


- (void)observeValueForKeyPath:(NSString *)keyPath
                      ofObject:(id)object
                        change:(NSDictionary<NSString *,id> *)change
                       context:(void *)context {
    if ([keyPath isEqualToString:@"rate"]) {
        float rate = [change[NSKeyValueChangeNewKey] floatValue];
        if (rate == 0.0) {
            _sessionStarted = NO;
            NSLog(@"Playback stopped");
        } else if (rate == 1.0) {

            if(!_sessionStarted) {

                LTSessionManager *sessionManager = [LTSessionManager sharedInstance];
                sessionManager.delegate = self;
                [sessionManager startSessionManager:self.playbackInfo];
                [sessionManager getSessionStatus];
                NSLog(@"Start session");
                _sessionStarted = YES;

            }
        } else if (rate == -1.0) {
            // Reverse playback
        }
    }
}

コントロールを削除するたびに- (void)observeValueForKeyPath:元に戻りますが、オブザーバーを取得できません。何か案は？前もって感謝します。