Thank You for your help. I solved it with "if ( !skView.scene ) {...}
":
- (void)viewWillLayoutSubviews
{
[super viewWillLayoutSubviews];
SKView * skView = (SKView *)self.view;
if ( !skView.scene ) { // <------- !!
SKScene * scene = [MenuScene sceneWithSize:skView.bounds.size];
scene.scaleMode = SKSceneScaleModeAspectFill;
[skView presentScene:scene];
}
}