You are not doing anything wrong.
This is a feature of the RadChart
called Sampling. You can read about it here
To improve performance when working with a huge number of items the RadChart combines (clusters) some of the items. It combines some items with close values and shows them as a single DataPoint (with average estimates for the X and Y).
You have control of how many DataPoints will be visualized by setting the SamplingThreshold
property. (By default it is 200).
In your case you might need to fully disable Sampling. To disable Sampling you need to set the SamplingThreshold
I hope this helps.
the Telerik team
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