To reproduce:
Add a RadChartView and use the following code:

public Form1()
{
    InitializeComponent();

    this.radChartView1.ShowTrackBall = true;
    this.radChartView1.ShowLegend = true;
    Random rand = new Random();
    var lineSeries = new LineSeries();
    for (int i = 0; i < 1000; i++)
    {
        lineSeries.DataPoints.Add(new CategoricalDataPoint(i, rand.Next(0, rand.Next(5, 20))));
    }
    radChartView1.Series.Add(lineSeries);
}

Workaround: change the LegendPosition:
this.radChartView1.ChartElement.LegendPosition = LegendPosition.Bottom;