Odd Portal nesting issue

I've never seen this sort of issue before. But the paginated report rendering is done by the webservice component of Report Server while a different process handles the rendering of pbix reports. So it would be worth checking either in the Report Server Configuration Manager or in the rsreportserver.config file to make sure that the webservice url (which normally defaults to /ReportServer ) is not pointing to the same address as the portal url (which normally defaults to /Reports). If the webservice url was changed to point to /Reports it *might* explain this behaviour as when the portal tried to ask the webservice to render a report it would end up pointing at itself.