UWP Delayed updates to Textbox using TraceListener

Question

I have a tracelistener:

public class WindowTraceListener : System.Diagnostics.TraceListener
{
    Model.TraceListener _value;
    public WindowTraceListener(Model.TraceListener value)
    {
        _value = nessusToChecklist;
    }
    public override void Write(string message)
    {
        _value.TraceOutput += message;
    }

    public override void WriteLine(string message)
    {
        _value.TraceOutput += (message + Environment.NewLine);
    }
}

And a POCO:

public class TraceListener: ObservableRecipient
{
    private string _TraceOutput;
    public string TraceOutput
    {
        get => _TraceOutput;
        set => SetProperty(ref _TraceOutput, value, true, "TraceOutput");
    }


}

Bound to a textbox:

    <Grid  Grid.Row="2" BorderBrush="Gray" BorderThickness="2" Margin="10,0">
        <ScrollViewer Name ="scrollTraceOutput"  >
            <TextBox Name="txtTraceOutput" TextWrapping="Wrap" Text="{Binding TraceListener.TraceOutput, UpdateSourceTrigger=PropertyChanged}" IsReadOnly="True" TextChanged="TextBox_TextChanged"  ></TextBox>
        </ScrollViewer>
    </Grid>

The problem is updates to the textbox are delayed and do not happen in realtime. I don't think I have a GUI thread issue, because if the process is long enough, updates to occur during processing. I just want the updates to occur faster.

For example, some processing has a ... and I want the "." to appear as it is traced.