Please double-check if you are not loading mismatching versions of CSS and JS files, especially of Telerik Kendo UI CSS and JS files. You can use the browser's console or Fiddler to record the requests and check if files have the same version.
The system requirements for using the HTML5 Report Viewer listed here can help you to verify the project fulfills the minimum required scripts versions.
Regards,
Stef
Telerik
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