AVCaptureDevice Low Light Boost Does Not Work After Release - ios

Question

I am working on a camera application that as a view controller, manager, and processor. The manager basically has AVCaptureSession, AVCaptureDeviceInput, and AVCaptureStillImageOutput to control image capture. Because the processor does a heavy image processing operations, I release the manager each time the image has been captured to avoid app crash.
I also have a button to toggle automaticallyEnablesLowLightBoostWhenAvailable (Low Light Settings) as documented by Apple here. Here's the toggle function:
- (IBAction)toggleLLBoost:(id)sender {
if([manager isLLBoostActivated]){
[self turnOffLLBoost];
} else {
[self turnOnLLBoost];
}
}
- (void)turnOffLLBoost
{
NSLog(#"LLBoost off");
[boostBt setSelected:NO];
[manager deactivateLLBoostMode];
[[[manager videoInput] device] removeObserver:self forKeyPath:#"lowLightBoostEnabled"];
}
- (void)turnOnLLBoost
{
NSLog(#"LLBoost on");
[boostBt setSelected:YES];
[manager activateLLBoostMode];
[[[manager videoInput] device] addObserver:self forKeyPath:#"lowLightBoostEnabled" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:NULL];
}
It will register observer when the Low Light Setting is ON, and remove observer when it's turned OFF. Here's the code in the manager that does the activation/deactivation for the setting:
-(void)activateLLBoostMode
{
AVCaptureDevice *device = [videoInput device];
if([device isLowLightBoostSupported]){
if([device lockForConfiguration:NULL]){
[device setAutomaticallyEnablesLowLightBoostWhenAvailable:YES];
[device unlockForConfiguration];
[self setIsLLBoostActivated:YES];
NSLog(#"Low Light Boost is set? %hhd",[device automaticallyEnablesLowLightBoostWhenAvailable]);
}
}
}
-(void)deactivateLLBoostMode
{
AVCaptureDevice *device = [videoInput device];
if([device isLowLightBoostSupported]){
if([device lockForConfiguration:NULL]){
[device setAutomaticallyEnablesLowLightBoostWhenAvailable:NO];
[device unlockForConfiguration];
[self setIsLLBoostActivated:NO];
NSLog(#"Low Light Boost is set? %hhd",[device automaticallyEnablesLowLightBoostWhenAvailable]);
}
}
}
Everything would work perfectly at first. The observer would get called when the lowLightBoostEnabled changed value. However, after I release the manager (session, device, output, etc.) and then re-setup the manager again upon finishing image processing, the observer would never get called. Despite the fact that 'automaticallyEnablesLowLightBoostWhenAvailable' has been set to YES.
Any advice or suggestion why this happens?
ADDITIONAL INFO:
Here's snippet of code of how manager initialized. After alloc/init setupSession will be called. At release, the dealloc method will be called:
-(BOOL)setupSession
{
[self deactivateLLBoostMode];
[self setIsLLBoostActivated:NO];
//Setting Session
[self setSession:[AVCaptureSession new]];
session.sessionPreset = AVCaptureSessionPresetPhoto;
//Setting Input
[self setVideoInput:[[AVCaptureDeviceInput alloc] initWithDevice:[self backFacingCamera] error:nil]];
if ([session canAddInput:videoInput]) {
[session addInput:videoInput];
}
//Setting Output
[self setStillImage:[AVCaptureStillImageOutput new]];
if ([stillImage isStillImageStabilizationSupported]) {
[stillImage setAutomaticallyEnablesStillImageStabilizationWhenAvailable:YES];
}
[stillImage setOutputSettings:#{AVVideoCodecKey: AVVideoCodecJPEG, AVVideoQualityKey:#0.6}];
if ([session canAddOutput:stillImage]) {
[session addOutput:stillImage];
}
return true;
}
-(void)dealloc
{
[session stopRunning];
self.session = nil;
self.stillImage = nil;
self.videoInput = nil;
self.toSaveImage = nil;
self.rawImages = nil;
}