Working UIBlurEffect and UIVisualEffectView masking example on iOS10 using ObjectiveC

AViewClass.m

// "self" in here is an UIView that contains some images inside.
{
  UIBlurEffect *blurEffect = [UIBlurEffect effectWithStyle:UIBlurEffectStyleLight];
  UIVisualEffectView *blurredEffectView = [[UIVisualEffectView alloc] initWithEffect:blurEffect];

  CGRect frame = self.frame;
  frame.origin = CGPointMake (0, 0);

  blurredEffectView.frame = frame;
  [self addSubview:blurredEffectView];

  UIView *maskView = [[UIView alloc] initWithFrame:frame];
  maskView.backgroundColor = [UIColor blackColor];

  __weak UIView *weak = self;
  maskView.layer.mask = ({ // This mask draws a rectangle and crops a circle inside it.
    __strong UIView *strong = weak;

    CGRect roundedRect = CGRectMake (
      0,
      0,
      strong.frame.size.width * 0.8f,
      strong.frame.size.width * 0.8f
    );
    roundedRect.origin.x = strong.frame.size.width / 2 - roundedRect.size.width / 2;
    roundedRect.origin.y = strong.frame.size.height / 2 - roundedRect.size.height / 2;

    CGFloat cornerRadius = roundedRect.size.height / 2.0f;

    UIBezierPath *path        = [UIBezierPath bezierPathWithRect:self.bounds];
    UIBezierPath *croppedPath = [UIBezierPath bezierPathWithRoundedRect:roundedRect cornerRadius:cornerRadius];
    [path appendPath:croppedPath];
    [path setUsesEvenOddFillRule:YES];

    CAShapeLayer *mask = [CAShapeLayer layer];
    mask.path     = path.CGPath;
    mask.fillRule = kCAFillRuleEvenOdd;
    mask;
  });

  blurredEffectView.maskView = maskView;
}

This works only if i present a view controller which has this, but doesnot work if i embed the viewcontroller in a navigation controller. Why? How can i prevent it