To reproduce:
            BarSeries barSeries = new BarSeries("Performance", "RepresentativeName");
            barSeries.DataPoints.Add(new CategoricalDataPoint(177, "Harley"));
            barSeries.DataPoints.Add(new CategoricalDataPoint(128, "White"));
            barSeries.DataPoints.Add(new CategoricalDataPoint(143, "Smith"));
            barSeries.DataPoints.Add(new CategoricalDataPoint(111, "Jones"));
            barSeries.DataPoints.Add(new CategoricalDataPoint(118, "Marshall")); 
            this.radChartView1.Series.Add(barSeries);

            LinearAxis verticalAxis = radChartView1.Axes.Get<LinearAxis>(1);
            verticalAxis.MajorStep = 5;
            LinearAxisModel axisModel = verticalAxis.Model as LinearAxisModel;
            
            AxisScaleBreak scaleBreakItem = new AxisScaleBreak();
            scaleBreakItem.Name = "Item1";
            scaleBreakItem.From = 80d;
            scaleBreakItem.To = 120d;
            verticalAxis.ScaleBreaks.Add(scaleBreakItem);

Use attached to reproduce. 

Workaround:
Use custom renderer: 

private void RadChartView1_CreateRenderer(object sender, ChartViewCreateRendererEventArgs e)
{
    e.Renderer = new CustomCartesianRenderer(e.Area as CartesianArea);
}

public class CustomCartesianRenderer : CartesianRenderer
{
    public CustomCartesianRenderer(CartesianArea area)
        : base(area)
    { }
    protected override void Initialize()
    {
        base.Initialize();
        for (int i = 0; i < this.DrawParts.Count; i++)
        {
            CartesianGridLineAnnotationDrawPart linePart = this.DrawParts[i] as CartesianGridLineAnnotationDrawPart;
            if (linePart != null)
            {
                this.DrawParts[i] = new MyCartesianGridLineAnnotationDrawPart((CartesianGridLineAnnotation)linePart.Element, this);
            }
        }
    }
}
class MyCartesianGridLineAnnotationDrawPart : CartesianGridLineAnnotationDrawPart
{
    public MyCartesianGridLineAnnotationDrawPart(CartesianGridLineAnnotation element, CartesianRenderer renderer)
       : base(element, renderer)
    { }
    public override void Draw()
    {
      
        PropertyInfo modelProperty = typeof(CartesianGridLineAnnotation).GetProperty("Model",
        System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic);
        object model = modelProperty.GetValue(this.Element);
        PropertyInfo layoutProperty = model.GetType().GetProperty("LayoutSlot", BindingFlags.Public | BindingFlags.Instance);
        RadRect radRect = (RadRect)layoutProperty.GetValue(model);
        RectangleF rect = ChartRenderer.ToRectangleF(radRect);


        rect.Offset(this.ViewportOffsetX, this.ViewportOffsetY);

        Graphics graphics = this.Renderer.Surface as Graphics;
       
        RadGdiGraphics radGraphics = new RadGdiGraphics(graphics);
        
        var clipRect = ChartRenderer.ToRectangle(this.Element.View.GetArea<CartesianArea>().AreaModel.PlotArea.LayoutSlot);
        clipRect.Offset((int)this.ViewportOffsetX,(int) this.ViewportOffsetY);

        graphics.SetClip(clipRect);
     

        GraphicsPath path = new GraphicsPath();
        path.AddLine(rect.Location, new PointF(rect.Right, rect.Bottom));

        BorderPrimitiveImpl border = new BorderPrimitiveImpl(this.Element, null);
        border.PaintBorder(radGraphics, null, path, rect);

        rect.Size = graphics.MeasureString(this.Element.Label, this.Element.Font);
        rect.Offset(this.Element.PositonOffset.Width + 1, this.Element.PositonOffset.Height + 1);

        TextParams tp = new TextParams();
        tp.font = this.Element.Font;
        tp.foreColor = this.Element.ForeColor;
        tp.paintingRectangle = rect;
        tp.text = this.Element.Label;

        TextPrimitiveHtmlImpl text = new TextPrimitiveHtmlImpl();
        text.PaintPrimitive(radGraphics, 0f, new SizeF(1f, 1f), tp);
    }
}

Please run the attached sample project.

Stack trace:
System.NullReferenceException occurred
  HResult=-2147467261
  Message=Object reference not set to an instance of an object.
  Source=Telerik.WinControls.ChartView
  StackTrace:
       at Telerik.Charting.CombinedBarSeriesRoundLayoutStrategy.ApplyLayoutRoundingVertical(LayoutContext context) in c:\Work\Development\RadControls\RadChartView\Engine\Series\Combination\BarSeries\CombinedBarSeriesRoundLayoutStrategy.cs:line 206
  InnerException: 

Currently, there is no built-in way to indicate an arbitrary area.

Currently, there is no way to increase the line thickness.

Use attached to reproduce. 

Workaround:

series.DataPoints.Add(new PieDataPoint(0.01, "Germany"));
series.DataPoints.Add(new PieDataPoint(0.01, "United States"));

 

To reproduce:
        public RadForm1()
        {
            InitializeComponent(); 

            this.radChartView1.AreaType = ChartAreaType.Polar;
            PolarAreaSeries polarAreaSeries = new PolarAreaSeries();
            PolarDataPoint polarPoint = new PolarDataPoint();
            polarPoint.Value = 35;
            polarPoint.Angle = 50;
            polarAreaSeries.DataPoints.Add(polarPoint);
            polarPoint = new PolarDataPoint();
            polarPoint.Value = 40;
            polarPoint.Angle = 200;
            polarAreaSeries.DataPoints.Add(polarPoint);
            polarPoint = new PolarDataPoint();
            polarPoint.Value = 55;
            polarPoint.Angle = 320;
            polarAreaSeries.DataPoints.Add(polarPoint);

            this.radChartView1.Series.Add(polarAreaSeries);
            
            this.radChartView1.Axes[0].LabelFitMode = AxisLabelFitMode.Rotate;
            AxisLabelElement gauche = this.radChartView1.Axes[0].Children[1] as AxisLabelElement;
            gauche.Text = "IV Gestion des ressources" + Environment.NewLine + "humaines";
            
          
              this.radChartView1.View.AxisLabelFormatting+=View_AxisLabelFormatting;
        }

        Font f = new Font("Arial", 10, FontStyle.Bold);

        private void View_AxisLabelFormatting(object sender, ChartAxisLabelFormattingEventArgs e)
        {
            if (e.LabelElement.Text.Contains("IV"))
            {
                e.LabelElement.Font = f;
            }
        }

After 1 million the decimal places of the labels are not correct, In your image. the labels on the horizontal axis go 999,992.50 - 999,995.00 - 999,997.5 -  1,000,000.00 - *1,000,003.00(should be 1,000,002.50) - 1,000,005.00 - *1,000,008.00(should be 1,000,007.5)

The same issue can be observed in a DPI-aware application on higher scaling
Workaround: set the RadControl.EnableDpiScaling property to false

public partial class Form1 : Form
{
    public Form1()
    {
        RadControl.EnableDpiScaling = false;

        InitializeComponent();

        LineSeries lineSeries = new LineSeries();
        lineSeries.DataPoints.Add(new CategoricalDataPoint(20, "Jan"));
        lineSeries.DataPoints.Add(new CategoricalDataPoint(22, "Apr"));
        lineSeries.DataPoints.Add(new CategoricalDataPoint(12, "Jul"));
        lineSeries.DataPoints.Add(new CategoricalDataPoint(19, "Oct"));
        this.radChartView1.Series.Add(lineSeries);

        LineSeries lineSeries2 = new LineSeries();
        lineSeries2.DataPoints.Add(new CategoricalDataPoint(18, "Jan"));
        lineSeries2.DataPoints.Add(new CategoricalDataPoint(15, "Apr"));
        lineSeries2.DataPoints.Add(new CategoricalDataPoint(17, "Jul"));
        lineSeries2.DataPoints.Add(new CategoricalDataPoint(22, "Oct"));
        this.radChartView1.Series.Add(lineSeries2);
        
        LassoZoomController lassoZoomController = new LassoZoomController();
        radChartView1.Controllers.Add(lassoZoomController);
    }

    private void radButton1_Click(object sender, EventArgs e)
    {
        this.radChartView1.ExportToImage(@"..\..\image.png", this.radChartView1.Size);
    }
}

To reproduce:
            DataTable table = new DataTable();
            table.Columns.Add("Value", typeof(double));
            table.Columns.Add("Name", typeof(string));
            table.Rows.Add(1, "John");
            table.Rows.Add(3, "Adam");
            table.Rows.Add(5, "Peter");
            table.Rows.Add(12, "Sam");
            table.Rows.Add(6, "Paul");

            BarSeries lineSeria = new BarSeries();
            radChartView1.Series.Add(lineSeria);
            lineSeria.ValueMember = "Value";
            lineSeria.CategoryMember = "Name";

            this.radChartView1.DataSource = table;

        private void radButton1_Click(object sender, EventArgs e)
        { 
            this.radChartView1.DataSource = null; 
        }

The chart data will be still visible. It is necessary to set explicitly the DataSource of the series:
this.radChartView1.Series[0].DataSource = null;

To reproduce:
- Add a chart to the form and set series with DataSource
- Close and dispose the form

Workaround:
Set the DataSource property of the series to null prior closing.

To reproduce: run the attached sample project and you will notice that the data points are not properly aligned.

Workaround: use equal number of data points for the series.

To reproduce: please refer to the attached sample project  and gif file illustrating the behavior on my end. 

Note: similar to the axis, the series should also have ClipLabels property which will control whether the labels will be clipped or not.

Workaround: use custom renderer:

 Sub New()

        InitializeComponent() 

        AddHandler Me.RadChartView1.CreateRenderer, AddressOf RadChartView1_CreateRenderer

        Dim barSeries As New Telerik.WinControls.UI.BarSeries("Performance", "RepresentativeName")
        barSeries.Name = "Q1"
        barSeries.ShowLabels = True
        barSeries.DataPoints.Add(New CategoricalDataPoint(177, "Harley"))
        barSeries.DataPoints.Add(New CategoricalDataPoint(128, "White"))
        barSeries.DataPoints.Add(New CategoricalDataPoint(143, "Smith"))
        barSeries.DataPoints.Add(New CategoricalDataPoint(111, "Jones"))
        barSeries.DataPoints.Add(New CategoricalDataPoint(118, "Marshall"))
        Me.RadChartView1.Series.Add(barSeries)
        Dim barSeries2 As New Telerik.WinControls.UI.BarSeries("Performance", "RepresentativeName")
        barSeries2.Name = "Q2"
        barSeries2.ShowLabels = True
        barSeries2.DataPoints.Add(New CategoricalDataPoint(153, "Harley"))
        barSeries2.DataPoints.Add(New CategoricalDataPoint(141, "White"))
        barSeries2.DataPoints.Add(New CategoricalDataPoint(130, "Smith"))
        barSeries2.DataPoints.Add(New CategoricalDataPoint(88, "Jones"))
        barSeries2.DataPoints.Add(New CategoricalDataPoint(109, "Marshall"))
        Me.RadChartView1.Series.Add(barSeries2)


        Dim lassoZoomController As New ChartPanZoomController()
        RadChartView1.Controllers.Add(lassoZoomController)

    End Sub
    
    Public Class CustomLabelElementDrawPart
        Inherits BarLabelElementDrawPart
        Public Sub New(owner As ChartSeries, renderer As IChartRenderer)
            MyBase.New(owner, renderer)

        End Sub

        Public Overrides Sub Draw()
            If Not Me.Element.ShowLabels Then
                Return
            End If

            Dim graphics As Graphics = TryCast(Me.Renderer.Surface, Graphics)
            Dim radGraphics As RadGdiGraphics = New RadGdiGraphics(graphics)
            Dim isSmartLabelsEnabled As Boolean = Me.Element.View.ShowSmartLabels
            Dim isLineToLabelEnabled As Boolean = Me.Element.DrawLinesToLabels

            For Each dataPointElement As DataPointElement In Me.Element.Children
                Dim categoricalDataPoint As CategoricalDataPoint = TryCast(dataPointElement.DataPoint, CategoricalDataPoint)


                For i As Integer = 0 To dataPointElement.Children.Count - 1
                    Dim labelElement As LabelElement = TryCast(dataPointElement.Children(i), LabelElement)

                    If labelElement Is Nothing Then
                        Continue For
                    End If

                    labelElement.OnLabelFormatting(New ChartViewLabelFormattingEventArgs(labelElement))

                    If Not labelElement.IsVisible OrElse String.IsNullOrEmpty(labelElement.Text) Then
                        Continue For
                    End If

                    Dim rect As Rectangle
                    Dim slot As RadRect = labelElement.GetLayoutSlot()

                    If isSmartLabelsEnabled AndAlso labelElement.SmartRectangle <> Rectangle.Empty Then
                        rect = labelElement.SmartRectangle
                    Else
                        slot = AdjustLayoutSlot(slot, labelElement.DataPointElement)
                        rect = ChartRenderer.ToRectangle(slot)
                    End If

                    Dim state As Object = radGraphics.SaveState()
                    Dim horizontalTranslate As Integer = rect.X + rect.Width / 2
                    Dim verticalTranslate As Integer = rect.Y + rect.Height / 2
                    Dim clipRect As RectangleF
                    If TypeOf Me.Renderer Is CartesianRenderer Then
                        Dim size As SizeF = graphics.MeasureString("W", Me.Element.Font)
                        Dim plotRect As RadRect = Me.Element.Model.LayoutSlot
                        plotRect.X += Me.ViewportOffsetX
                        plotRect.Y += Me.ViewportOffsetY
                        clipRect = ChartRenderer.ToRectangleF(plotRect)
                        clipRect.Y -= size.Height / 2.0F
                        clipRect.Height += size.Height
                        clipRect.Width += size.Width * 2.0F
                        graphics.SetClip(clipRect)
                    End If

                    Dim angle As Single = CSng(Me.Element.LabelRotationAngle) Mod 360.0F

                    If angle <> 0 Then
                        radGraphics.TranslateTransform(horizontalTranslate, verticalTranslate)
                        radGraphics.RotateTransform(angle)
                        radGraphics.TranslateTransform(-horizontalTranslate, -verticalTranslate)
                    End If

                    If isLineToLabelEnabled Then
                        Me.DrawConnectingLine(radGraphics, labelElement, dataPointElement, isSmartLabelsEnabled AndAlso labelElement.SmartRectangle <> Rectangle.Empty)
                    End If

                    If labelElement.BackgroundShape IsNot Nothing Then
                        labelElement.BackgroundShape.Paint(CType(radGraphics.UnderlayGraphics, Graphics), rect)
                    End If

                    Dim fill As Telerik.WinControls.Primitives.FillPrimitiveImpl = New Telerik.WinControls.Primitives.FillPrimitiveImpl(labelElement, Nothing)
                    fill.PaintFill(radGraphics, 0, System.Drawing.Size.Empty, rect)
                    Dim border As Telerik.WinControls.Primitives.BorderPrimitiveImpl = New Telerik.WinControls.Primitives.BorderPrimitiveImpl(labelElement, Nothing)
                    border.PaintBorder(radGraphics, 0, System.Drawing.Size.Empty, rect)

                    Using brush As Brush = New SolidBrush(labelElement.ForeColor)
                        Dim drawRectangle As RectangleF = New RectangleF()
                        drawRectangle.X = rect.X + labelElement.Padding.Left
                        drawRectangle.Y = rect.Y + labelElement.Padding.Top
                        drawRectangle.Width = rect.Width - labelElement.Padding.Right
                        drawRectangle.Height = rect.Height - labelElement.Padding.Bottom
                        Dim format As StringFormat = New StringFormat()
                        format.Alignment = ContentAlignmentToHorizontalStringAlignment(labelElement.TextAlignment)
                        format.LineAlignment = Me.ContentAlignmentToVerticalStringAlignment(labelElement.TextAlignment)
                        graphics.DrawString(labelElement.Text, labelElement.Font, brush, drawRectangle, format)
                    End Using

                    If angle <> 0 Then
                        radGraphics.ResetTransform()
                        radGraphics.RestoreState(state)
                    End If

                    graphics.ResetClip()
                Next
            Next
        End Sub

        Public Function ContentAlignmentToVerticalStringAlignment(ByVal contentAlignment As ContentAlignment) As StringAlignment
            Dim result As StringAlignment

            Select Case contentAlignment
                Case contentAlignment.BottomCenter, contentAlignment.BottomLeft, contentAlignment.BottomRight
                    result = StringAlignment.Far
                Case contentAlignment.TopCenter, contentAlignment.TopLeft, contentAlignment.TopRight
                    result = StringAlignment.Near
                Case Else
                    result = StringAlignment.Center
            End Select

            Return result
        End Function

        Private Function ContentAlignmentToHorizontalStringAlignment(ByVal contentAlignment As ContentAlignment) As StringAlignment
            Dim result As StringAlignment

            Select Case contentAlignment
                Case contentAlignment.BottomLeft, contentAlignment.MiddleLeft, contentAlignment.TopLeft
                    result = StringAlignment.Near
                Case contentAlignment.BottomRight, contentAlignment.MiddleRight, contentAlignment.TopRight
                    result = StringAlignment.Far
                Case Else
                    result = StringAlignment.Center
            End Select

            Return result
        End Function

    End Class

    Private Sub RadChartView1_CreateRenderer(sender As Object, e As ChartViewCreateRendererEventArgs)
        e.Renderer = New CustomCartesianRenderer(e.Area)
    End Sub

    Public Class CustomCartesianRenderer
        Inherits CartesianRenderer
        Public Sub New(area As CartesianArea)
            MyBase.New(area)
        End Sub
        Protected Overrides Sub Initialize()
            MyBase.Initialize()
            For i As Integer = 0 To Me.DrawParts.Count - 1

                Dim label As BarLabelElementDrawPart = TryCast(Me.DrawParts(i), BarLabelElementDrawPart)
                If (label IsNot Nothing) Then
                    Me.DrawParts(i) = New CustomLabelElementDrawPart(label.Element, Me)
                End If
            Next
        End Sub
    End Class

Create a chart with a LinesSeries with a DateTimeContinuousAxis axis and set the following properties:
DateTimeContinuousAxis horizontalAxis = new DateTimeContinuousAxis();
horizontalAxis.Title = tupleItem.HorizontalAxis;
horizontalAxis.AxisType = AxisType.First;
horizontalAxis.VerticalLocation = AxisVerticalLocation.Bottom;
horizontalAxis.AutomaticBorderColor = false;
horizontalAxis.MaximumTicks = 10;
horizontalAxis.LabelFormat = "{0:HH:mm:ss.fff}";

You will see that there are less labels than ticks.

When the chart is zoomed the labels also disappear from the ticks.

Add Three Line Break Series to RadChartView

Currently, ScatterSeries are able to use NumericAxes only. A good improvement will be to allow using DateTimeContinuousAxes as well.

To reproduce use the following code to initialize the chart:

DataTable dt = new DataTable();
dt.Columns.Add("Category", typeof(string));
dt.Columns.Add("Value", typeof(int));
dt.Rows.Add("010010", 5);
dt.Rows.Add("000020", 6);
dt.Rows.Add("000030", 2);
dt.Rows.Add("000040", 11);
return dt;

BarSeries bs = new BarSeries("Value", "Category");
bs.Palette = new PaletteEntry(Color.BlanchedAlmond);
radChartView1.DataSource = dt;
radChartView1.Series.Clear();
radChartView1.Series.Add(bs);
radChartView1.GetArea<CartesianArea>().Orientation = Orientation.Horizontal;

Workaround:
CategoricalAxis Axis = radChartView1.Axes.Get<CategoricalAxis>(1);
Axis.LabelFormat = "{0:000000}";

Axes should allow custom formatting for each individual label. Consider the following scenario - a chart provides information for each hour of the day. Each label should contain only the hours data, however, when the date changes the label should contain the full date information.

HeightAspectRatio affects the height of BarSeries even when the area has a horizontal orientation

Add null value support for RadChartView