SimpleDataField - return from compute() crashes simulator for Epix Pro (Gen 2) 51mm Amelod

I've just updated my data field app to try and support the 3 new types of Epix watches.

            <iq:product id="epix2pro42mm"/>
            <iq:product id="epix2pro47mm"/>
            <iq:product id="epix2pro51mm"/>
The first two are fine; however for that last one, the  Epix Pro (Gen 2) 51mm Amelod crashes the simulator on return from the compute function.
My minimal example that demonstrates this is
    function compute(info as Activity.Info) as Numeric or Duration or String or Null {
        var timeUsed    = new Time.Duration(6000) ;
        return timeUsed.value() ;
    }
In every other case this works fine - but for this one watch it crashes when the return is executed.
If I change the return to a string or a number it's all fine but the Duration seems to break it.  Is this a limitation of the watch that I need to work around in code or an bug with the simulation?
I'm developing on Windows 11 using VScode  1.84.1 and version 1.0.9 of the Garmin extension so the latest versions and also the latest 6.3.1 SDK.