Spritekit scene not visible in Watchkit table row

Question

I have a SpriteKit scene that I want to show a progress ring, in each row of a table. However, the scene is not visible. I have tried it outside of a table so I know the RingScene is working ok, but I cannot get it to show in the table row. The row has a group, but they are clear colour so I don't think they are obscuring it. The code I have is: thanks if you can suggest something.

import WatchKit
import Foundation

class DevicesController: WKInterfaceController {

@IBOutlet var deviceTable: WKInterfaceTable!

// for ring
var scene: RingScene!

override func awake(withContext context: Any?) {
    super.awake(withContext: context)
    refreshTable()
}

func refreshTable() {
    deviceTable.setNumberOfRows(1, withRowType: "DevicesRowType")

    for index in 0..<deviceTable.numberOfRows {

        if let controller = deviceTable.rowController(at: index) as? DevicesRC {
            controller.rowNumber = index
            controller.delegate = self

            // SceneKit
            scene = RingScene(size: contentFrame.size)
            controller.skInterface.presentScene(scene)
        }
    }
}

and Row Controller is:

import WatchKit

protocol DeviceRowDelegate {
    func rowSettingsButtonConnect(atIndex: Int)
    func rowSettingsButtonDisconnect(atIndex: Int)
    func rowSwitch(atIndex: Int)
}

class DevicesRC: NSObject {

    @IBOutlet var skInterface: WKInterfaceSKScene!
}