TableView not updating bindings when changed programmatically?

So I have a settings panel in my app that uses a TableView and Cells to show various options to users. There are EntryCell and SwitchCell items in the TableView. These Cells are data bound to a ViewModel.

Decided to add a "Reset to Defaults" button on the settings page. Pressing it, as you might expect, programmatically changes all the settings values in the app to their original, unedited states. When I try this, however, the values displayed do not appear to change at all. EntryCells retain their edited text, and SwitchCells remain in their previous states. If I close the settings page, go back to the main app, then recreate the settings page, of course, the values all reflect their defaults. I tried utilizing ForceLayout on the settings page, but it doesn't appear to change the behavior at all.

This is on Android by the way, actual devices or simulators. I haven't tried in iOS yet...

Is there a means to get the TableView to update itself? I even tried resetting its BindingContext to null, perform the data reset, then set the BindingContext back, but even that doesn't make it update itself...

Xaml looks like this:

        <StackLayout>
            <TableView Intent="Settings" x:Name="tblSet" >
                <TableView.Root>
                    <TableRoot>
                        <TableSection Title="Server Settings">

                                <EntryCell x:Name="ecServer" Label="URL:" Placeholder ="Required Server Address" />

    ...other entrycells and switchcells here...

                        </TableSection>
                    </TableRoot>
                </TableView.Root>
            </TableView>
            <Button Text="Reset" x:Name="btnReset" VerticalOptions="End" HorizontalOptions="Center" />
        </StackLayout>  

The bound data is a class with Strings and booleans, nothing fancy. For example:

    public class UserSettings : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        /// <summary>
        /// Update any bindings that a given value has changed.
        /// </summary>
        /// <param name="propertyName">The property that changed, by name.</param>
        private void OnPropertyChanged( [CallerMemberName] String propertyName = "" )
        {
            var handler = PropertyChanged;
            if( handler != null )
            {
                handler( this, new PropertyChangedEventArgs( propertyName ) );
            }
        }

        private static readonly UserSettings instance = new UserSettings();
        public static UserSettings Instance
        {
            get { return instance; }
        }

        private String _serverUri;
        public String ServerURI 
        {
            get { return _serverUri; }
            set
            {
                if( _serverUri != value )
                {
                    _serverUri = value;
                    OnPropertyChanged();
                }
            }
        }

        public void ResetAll()
        {
            ServerURI = String.Empty;
...
    }

}

For the settings page:

    public class SettingsPage : ContentPage
    {
            UserSettings _us;

            public SettingsPage()
            {
                ...initialization...

                _us = UserSettings.Instance;
                tblSet.BindingContext = _us;
                ecServer.SetBinding( EntryCell.TextProperty, "ServerURI" );

                btnReset.Clicked += btnReset_Clicked;

... other setup....
            }


        public async void btnReset_Clicked( object sender, EventArgs e )
        {
            bool bAnswer = await DisplayAlert( "", "Resetting will clear all user settings and data.  Do you wish to perform the reset?", "Yes", "No" );
            if( bAnswer == true )
            {
                _us.ResetAll();
                ForceLayout();
            }
        }
}