Errors with SCISplineLineRenderableSeries while zooming

SciChart 3.1.0.5175 running on iOS 13.6

Please see this short video which demonstrates the issue: https://youtu.be/HjtWZDZeyXM

I have a chart showing a single Spline data series. The data series never drops below zero, yet the chart shows multiple points where the line drops below zero as you zoom in and out. This behavior changes as the zoom level changes.

Is this expected behavior for the spline chart? Is there a way to change the behavior so the chart does not show these sub-zero points?

private func drawChart()
{
    createChartSurface()

    let series = self.getPositionSeries( name: name, color: color, results: resultsSession.rearResults )
    self.sciChartSurface?.renderableSeries.add(series)


}


private func createChartSurface()
{
    // If we created a chart surface previously then we need to remove it from the superview
    sciChartSurface?.removeFromSuperview()

    // Create a SCIChartSurface. This is a UIView so can be added directly to the UI
    sciChartSurface = SCIChartSurface()
    sciChartSurface?.translatesAutoresizingMaskIntoConstraints = false
    self.view.addSubview(sciChartSurface!)

    //sciChartSurface?.autoresizingMask = [.flexibleHeight, .flexibleWidth] // chart bottom falls off the view without this
    sciChartSurface?.topAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.topAnchor).isActive = true
    sciChartSurface?.bottomAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.bottomAnchor).isActive = true
    sciChartSurface?.leftAnchor.constraint(equalTo: self.view.leftAnchor).isActive = true
    sciChartSurface?.rightAnchor.constraint(equalTo: self.view.rightAnchor).isActive = true

    // Create an XAxis and YAxis. This step is mandatory before creating series
    let xaxis = SCINumericAxis()
    xaxis.axisTitle = "Seconds"
    sciChartSurface?.xAxes.add(xaxis)

    let yaxis = SCINumericAxis()
    yaxis.axisTitle = "Position (mm)"
    yaxis.axisId = "p" // position
    yaxis.axisAlignment = .right
    sciChartSurface?.yAxes.add(yaxis)

    let yaxis = SCINumericAxis()
    yaxis.axisTitle = "Speed mm/s"
    yaxis.axisId = "s" // speed
    yaxis.axisAlignment = .left
    sciChartSurface?.yAxes.add(yaxis)


    addModifiers()
}


private func getPositionSeries( name: String, color: UIColor, results: ResultData ) -> SCISplineLineRenderableSeries
{
    let positionData = SCIXyDataSeries(xType: .double, yType: .double)
    positionData.seriesName = name
    let start = resultsSession.indexStart + 1
    let last = resultsSession.indexEnd

    for index in start ... last {
        let t1 = resultsSession.sensorData[index-1].time
        let t2 = resultsSession.sensorData[index].time
        if ((t2-t1) == 1) {
            let x = Double(t2) / resultsSession.sampleRate
            let y = results.axleData[index].position
            positionData.append(x: x, y: y)
        } else {
            // There was a gap in the data.  Fill in the gap with a horizontal line.
            let y = results.axleData[index-1].position
            for tx in (t1 + 1) ... t2 {
                let x = Double(tx) / resultsSession.sampleRate
                positionData.append(x:x, y:y)
            }
        }
    }

    let positionSeries = SCISplineLineRenderableSeries()  // SCIFastLineRenderableSeries()
    positionSeries.dataSeries = positionData
    positionSeries.yAxisId = "p"
    positionSeries.strokeStyle = SCISolidPenStyle(color: color, thickness: 1.0)
    return positionSeries
}