Bike speed sensor on Edge 830 not working

I have a ConnectIQ app which reads from a bike speed/cadence sensor on Edge520plus, and on Edge830 simulator, but not in on real Edge830.  I have tried using ANT plus, and also the sensor object. Stranger still, it works on Edge830 if I swap the BIKESPEED sensor for BIKEPOWER.  

I have posted this as a question on the discussion forum, but received no answer.

Here is my simplified code, modified from Sensor example.  I have all permissions enabled, just in case..

using Toybox.WatchUi;
using Toybox.Graphics;
using Toybox.System as Sys;
using Toybox.Lang;
using Toybox.Time.Gregorian;
using Toybox.Sensor;
using Toybox.Application;
using Toybox.Position;

class SensorTester extends WatchUi.View
{
    var string_SPD;
    var SPD_graph;

    //! Constructor
    function initialize()
    {
        View.initialize();
        Sensor.setEnabledSensors( [Sensor.SENSOR_BIKESPEED] );
        Sensor.enableSensorEvents( method(:onSnsr) );
        string_SPD= "---kph";
    }

    //! Handle the update event
    function onUpdate(dc)
    {
        dc.setColor(Graphics.COLOR_BLACK, Graphics.COLOR_BLACK);
        dc.clear();
        dc.setColor(Graphics.COLOR_WHITE, Graphics.COLOR_TRANSPARENT );
        dc.drawText(dc.getWidth() / 2, 90, Graphics.FONT_LARGE, string_SPD, Graphics.TEXT_JUSTIFY_CENTER);
    }

    function onSnsr(sensor_info)
    {
        var SPD = sensor_info.speed;
        if( SPD != null )
        {
        	Sys.println("Spd = " + SPD.toString());
            string_SPD = SPD.toString() + "kph";
        }
        else
        {
            string_SPD = "---kph";
            Sys.println("SPD = null");
        }

        WatchUi.requestUpdate();
    }
}

//! main is the primary start point for a Monkeybrains application
class SensorTest extends Application.AppBase
{
    function initialize() {
        AppBase.initialize();
    }

    function onStart(state)
    {
        return false;
    }

    function getInitialView()
    {
        return [new SensorTester()];
    }

    function onStop(state)
    {
        return false;
    }
}