Robohelp 2017 - Webhelp - Calling topic with URL not working in IE 11

Converting projects from Robohelp 10 to 2017. Discovered using this type of URL eg: X:/helpfolder/startpage.htm#path/target_topic_1.htm (reference to this info http://www.grainge.org/pages/authoring/calling_webhelp/using_urls.htm )  does not work properly in IE 11 but does in Google Chrome.

In IE 11, the full topic page displays with the Show link - but without the TOC/Search panes.  The Show link returns the default home page along with the TOC/Search pane - not the topic page.

Any help out there would be appreciated.