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I would like to clarify that we are not aware of such issue. Could you please clarify whether you are applying template at run-time? If yes - could you please share how exactly you are applying the the templates to the nodes added in the node expand server-side event handler and whether you are applying the template to all existing nodes in the Page_Load event handler as shown in this help article
If you are not using templates then I assume that you simply set the RadTreeView Checkboxes property to true. In this case reloading the page should not affect to the check boxes. For reference I attached a sample project that has the RadTreeView Checkboxes enabled and implements very similar scenario.
Hope that this will be helpful.
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