iOS ARKit state (cameraDidChangeTrackingState) stuck in initializing, doesn't track

Question

Apologies for the newb question in advance (can't find it elsewhere on SO), but has anyone had problems in getting any and/or all the ARKit demos to initialize?

Take for example, the default / vanilla app - what you get when you create an empty ARKit project. What I see is the ship hovering above the default view port, and when I pan, it stays pretty much centered in the viewport and not fixed in space, I cannot move above or to the sides of the spaceship. When I look at the camera state property in cameraDidChangeTrackingState, it shows "limited / initializing, but never changes from that. I feel like I must be missing something obvious, like perhaps an entitlement - or some other device level setting?

func session(_ session: ARSession, cameraDidChangeTrackingState camera: ARCamera) {
    switch camera.trackingState {
    case .notAvailable:
        print("Tracking: not available: \(camera.trackingState)")
    case .limited(let reason):
        print("Tracking limited: \(reason)") <-- only gets here, with "initializing"
    case .normal:
        print("tracking normal: \(camera.trackingState)")
    }
}

For what it's worth, I am using Xcode 9.0, and an iPhone 8.

Thanks!

Answer 1

As odd as it seemed, simply restarting the phone fixed the problems on all the apps that I was seeing. I have no idea what went wrong or why though.