Storyline published to the web - Terminating the 'course' and returning to the 'start page'

Hi

I publish courses on the web.

To include Storyline output along with the video, text, quizzes, etc., I publish my storyline and Rise files to the web and then add a link to them from my course web page.

My question concerns how to terminate Storyline 'session'.

The Storyline course contains a button, 'Return to course' with two actions when user clicks it:

1. Exit course (only 2 slides but I guess its a course in SL terms)

2. Open (url) (To return to my web course)

in that order.

Everything works as required but when I next click the link to the SL 'course', I am shown a button labelled, 'Resume' in the middle of a black screen.

This seems that I did not manage to end the (Storyline) 'course'.

I'd be interested in feedback.

Thanks

Steve