Overlay SKScene is not showing

I'm trying to overlay an SKScene over a SCNScene. When I run my app on the simulator and an iPhone6+, the overlayScene(SKScene) is shown as intended, but when I tried running it on the iPhone5 (tried 2 different devices) the overlayScene does not appear.

Does anyone have an idea why? Both device run on iOS 9.2.1. I have only tested the app on those two models. Here's my code inside the GameViewController.Swift

    //Configure the view
    sceneView = self.view as? SCNView

    //Configure the scene
    sceneView.scene = gameScene
    sceneView.playing = true
    sceneView.backgroundColor = UIColor.blackColor()
    sceneView.antialiasingMode = SCNAntialiasingMode.Multisampling4X

    let overlayScene = OverlayScene(size: self.view.bounds.size)
    sceneView.overlaySKScene = overlayScene

Thanks!