I wasn't able to reproduce your issue. Could you send us a runnable copy of your project where this issue is reproducible or edit the sample I have attached.
Could you also try setting your chart's IntelligentLabelsEnabled="true" and AutoLayout="true".
You can also refer to our empty values demo example here and our help topic here to find more information about the empty values feature.
Regards,
Peshito
the Telerik team
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