When an external user (snc_external role) views the Report widget which is displaying a published report they get "Security constraints prevent access to requested page" instead of the report.
The user does not have access to the report_viewer ui_page which we use to display the report in the widget. Also it needs to have read access to the sys_report table and review_view access to the table where the data in the report comes from
*Note: please also add other roles that need to access corresponding reports to this ACL e.g. itil or snc_internal, depends on your actual requirement. Otherwise, users without the snc_external role will not be able to access those reports after adding the ACL. This behavior is working as how the report_view ACL designed*