It has been a while.
Just now I performed a 'node upgrade' which went without problems but now when I run a preview of our courses the window remains blank (not even the loader is visible). When I change the main.html from the link in the browser (FF) to index.html all is well.
We used to have this problem because of the 'Spoor' component and then we upgraded this from 2.0.6 to 2.0.7 and it was solved. Now the plugin is 2.0.9 which should be the most recent one. What can I do to solve this issue?