info.currentPower is null on my 920xt

I'm having trouble with info.currentPower in a data field. It works fine in the simulator, but on my 920xt, it seems to always be null. I created the test field below to isolate the issue. It displays "--" before and during an activity even when the built in power fields (i.e. power, 3s avg power) display correctly. Also, info.averagePower works fine (during an activity).

My 920xt has software version 3.07, and I'm using CIQ SDK 1.1.0. Thanks in advance for any help.

using Toybox.WatchUi as Ui;

class PowerTestView extends Ui.SimpleDataField {

//! Set the label of the data field here.
function initialize() {
label = "My Label";
}

//! The given info object contains all the current workout
//! information. Calculate a value and return it in this method.
function compute(info) {
// See Activity.Info in the documentation for available information.
if (info.currentPower == null)
{
return "--";
}
else
{
return info.currentPower;
}
}
}