The legend is a part of the SVG rendering of the chart and thus HTML entities should not be used there. If such special symbols are present, they will break the code structure and unexpected effects will appear. Thus, I am afraid that the legend cannot show such special symbols. The less than (<) will initiate an opening tag which will cause problems. If they are present in the datasource passed to the chart, I advise that you remove them (e.g., a replace before passing the datasource).
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