ThrottleLast not working reliably on MAUI using defaults

[gerdus]

This code does not work reliably (only reports a few values and then stops):

        docsyncsub = syncStateModel.DocumentsToSyncCount.ThrottleLast(TimeSpan.FromSeconds(3)).Subscribe((x) =>
        {
            Dispatcher.Dispatch(() =>
            {
                lblDebugDocCount.Text = $"{x}";
            });
        });

while this does work reliably:

        docsyncsub = syncStateModel.DocumentsToSyncCount.ThrottleLast(TimeSpan.FromSeconds(3), TimeProvider.System).Subscribe((x) =>
        {
            Dispatcher.Dispatch(() =>
            {
                lblDebugDocCount.Text = $"{x}";
            });
        });

syncStateModel.DocumentsToSyncCount is R3.BindableReactiveProperty
I have the UseR3 on builder in CreateMauiApp

Or is there something I am doing wrong or not understanding?

Thank you.