We are trying to make our website accessible using Wave and one thing we are struggling with is TreeViews with checkboxes enabled. Sometimes the checkbox is rendered as a span element and sometimes as an input element. In the second case Wave is recognizing an error for each node as the input element is not associated with its neighbouring text. You can see this on your own website: https://demos.telerik.com/aspnet-ajax/treeview/examples/functionality/checkboxes/defaultcs.aspx. For the server side tree the checkboxes are rendered as inputs and there is no label associated with it.

This behaviour doesn't change when I set EnableAriaSupport="true".