Asp.Net RDLC performance issue

I was recently worked on very interesting issue in RDLC.Few months back the application migrated from 3.5 to 4.6 and deployed in the production and working good.Recently few users are reported, page not responding to any action on the page even cancel button click in the application.Started  investigating on the issue.Initial i was think it may  due to data but later on  due to migration and the solution is to add below value in web.config.

      <trust legacyCasModel=”true” level=”Full”/>