Camera preview becomes slow - AVFoundation

Device: iPad Pro 10.5-inch

IOS: 10.3.2 10.3.3

I use the following function to take a snapshot in the app.

UIView (UISnapshotting)
  - (BOOL) drawViewHierarchyInRect: (CGRect) rect afterScreenUpdates: (BOOL) afterUpdates;

CGRect rect = self.view.bounds;
UIGraphicsBeginImageContextWithOptions(rect.size, NO, [[UIScreen mainScreen] scale]);
[self.view drawViewHierarchyInRect:rect afterScreenUpdates:YES];

UIImage *snapshot = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

However, every time I use this feature, the Camera preview rendering by AVFoundation used in another part of the application became slow.

    self.session = [[AVCaptureSession alloc] init];

    AVCaptureDevice *camera = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];

    self.input = [[AVCaptureDeviceInput alloc] initWithDevice:camera error:&error];
    [self.session addInput:self.input];

    self.output = [[AVCapturePhotoOutput alloc] init];
    [self.session addOutput:self.output];

    self.prevLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:self.session];
    self.prevLayer.frame = self.previewView.layer.bounds;
    self.prevLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
    switch ([[UIApplication sharedApplication] statusBarOrientation]) {
        case UIInterfaceOrientationLandscapeLeft:{
            AVCaptureConnection *con = self.prevLayer.connection;
            con.videoOrientation = AVCaptureVideoOrientationLandscapeLeft;
        }
            break;
        case UIInterfaceOrientationLandscapeRight:{
            AVCaptureConnection *con = self.prevLayer.connection;
            con.videoOrientation = AVCaptureVideoOrientationLandscapeRight;
        }
            break;
        case UIInterfaceOrientationPortrait:{
            AVCaptureConnection *con = self.prevLayer.connection;
            con.videoOrientation = AVCaptureVideoOrientationPortrait;
        }
            break;
        case UIInterfaceOrientationPortraitUpsideDown:{
            AVCaptureConnection *con = self.prevLayer.connection;
            con.videoOrientation = AVCaptureVideoOrientationPortraitUpsideDown;
        }
            break;
        default:
            break;
    }

    [self.previewView.layer addSublayer:self.prevLayer];

    [self.session startRunning];

Currently we are seeing this problem only in the above device and OS environment.

Anyone can solve this? I need information that will lead to resolution.