I am afraid we are not aware of such issue with the control. I have attached a small example, based on your code. Can you please run it and observe the output window, where you should see the count of selections/deselections.
I noticed that you have set both Palette and PaletteName properties. In this case the chart will only respect the value of Palette, but that does not seem to be related to the behavior you observe. I am not sure if I can provide you with any clues apart from the obvious -- make sure that the chart is not overlapped by another control or a layer which handles the clicks/taps. As an addition, you can set the SelectionPalette or SelectionPaletteName property of the control. This will provide you with a visual clue if the item is actually selected.
Finally, if you are able to reproduce the problem in a stand-alone runnable project (or modify the attached example), please open a support ticket and send it to us, so that we can investigate it.
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