Thank you for providing another image. It is hard to really determine what is going without your actual code, however in this new image it appears that label for the value is not being shown because there is not enough room left to display the label.
For instance, all the other gray values are displayed because there is room between the end of the blue range and the top of the chart. In columns 1,2 and 4 there is no room left over. Except for the first category (green), the label will appear in its own section of the bar. So if you have a value that is a few percent and at the top of the chart, the label wont display.
You could create your own custom Style for the ItemLabel you can find instructions on that here
, but you may end up needed to edit the entire control template to allow the value to show even when there is no room. This link
will bring you to the Styling Overview for the entire RadChart. To learn how to extract the entire control template, this link
will demonstrate that for you.