This looks like a bug that appears in application initialization. Could you also try to create a user control and see what will be returned with the code below
var pageMan = PageManager.GetManager("OpenAccessDataProvider");
var node = pageMan.GetPageNodes().FirstOrDefault(n => n.Name.Equals("BackendSiteMap", StringComparison.OrdinalIgnoreCase));
Could you delete the config files inside App_Data/Sitefinity/Configuration folder. This will re initialize the project again and you have to install it again.
All the best,
the Telerik team
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