To reproduce:

private void RadChartView1_LabelFormatting(object sender, ChartViewLabelFormattingEventArgs e)
{
    var dataPoint = e.LabelElement.DataPoint as CategoricalDataPoint;
    if (dataPoint != null)
    {
         e.LabelElement.IsVisible = false;
    }
}

Workaround:
private void RadChartView1_LabelFormatting(object sender, ChartViewLabelFormattingEventArgs e)
{
    var dataPoint = e.LabelElement.DataPoint as CategoricalDataPoint;
    if (dataPoint != null)
    {
        e.LabelElement.Text = "";
    
    }
}