See this forum thread for reproducible and workaround: http://www.telerik.com/community/forums/legend-will-only-display-labels-(windows-10)

When using shp and dbf files with ~130MB size, it takes minutes to load the map

When you have several series(ScatterLineSeries reported but it happens with others as well) in the RadCartesianChart and you clear the Items of one of them by calling the Clear() method - the line is not redrawn and it shows the old data. 

It should be similar like the RealizedItemsVerticalBufferScale, but to work for the horizontal part of the ViewPort.

I am trying to use the chart control in multiple views: Meaning not just one window. I create several windows from the main window. It is not call "windows". It is a view.

It looks like the chart control fails:

System.Exception: The application called an interface that was marshalled for a different thread. (Exception from HRESULT: 0x8001010E (RPC_E_WRONG_THREAD))
   at Windows.UI.Xaml.Media.SolidColorBrush.get_Color()
   at Telerik.UI.Xaml.Controls.Chart.ContainerVisualsFactory.ChangeBrushesAccordingToAppTheme()
   at Telerik.UI.Xaml.Controls.Chart.ContainerVisualsFactory.PrepareCartesianAxisLineVisual(CartesianAxis axis, ContainerVisual lineContainer, RadRect layoutSlot, AxisType axisType)
   at Telerik.UI.X

Is there a way to fix it ?

to understand the concept of multiple views:

https://docs.microsoft.com/en-us/windows/uwp/design/layout/show-multiple-views

please advise me...