Below is quote from my response in support ticket #877256
"On your question, please go through the steps listed in the How To: Use ASP.NET MVC Report Viewer in an application article and verify all settings are applied correctly after the upgrade. Also note that there are minimum system requirements for using the HTML5 Report Viewer and Reporting REST service.
If you have an MVC4+ application, double-check the webpages:Version in the web.config file."
If you need further help, please use this account to open a support ticket with demo project isolating and reproducing the problem.
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