FastLineRenderableSeries sometimes not updating when data is appended.

I have the following SciChart surface in my program:

<s:SciChartSurface
            Name="Chart"
            Margin="0,0,4,0"
            Padding="0"
            BorderThickness="0"
            GridLinesPanelStyle="{StaticResource SciChartBackgroundStyle}">
            <s:SciChartSurface.RenderableSeries>
                <s:FastLineRenderableSeries
                    x:Name="LevelSeries"
                    DataSeries="{Binding Series}"
                    ResamplingMode="None"
                    Stroke="{StaticResource LabelColor}"
                    StrokeThickness="1" />
            </s:SciChartSurface.RenderableSeries>
        </s:SciChartSurface.RenderableSeries>

         <!-- Axis and modifiers snipped for readability -->
</s:SciChartSurface>

In my ViewModel I have a public XyDataSeries<DateTime, short> Series property. We do custom decimation on zoom, so when the chart is zoomed, the Series is cleared and repopulated with Series.Append in chunks.

My issue is that some of the time, the final .Append does not trigger a redraw. The data is in the series, the mouse rollover works and I can “see” the data, but it isn’t drawn.

Forcing the redraw using ViewportManager.InvalidateElement(); works but i would obviously prefer to not have to do that.

I would estimate that this issue happens ~1/5 times.

I’ve attached a gif showing the issue.