Thank you for the video. The warning about no pages in the questionnaire seems to appear immediately after you open the print view, nothing seems to change when you click the "JavaScript" button.
The most likely explanation seems to be that there is actually no (visible) content on the first page of the *_W0_START questionnaire?!
In the video there was no error message about the survey being over. However, that may occur when you had the preview open too long. The preview token may expire, and then any other call to the URL may just send you to the "normal" questionnaire URL.
We had extended this period recently (from 30 seconds to 5 minutes), which may explain why you encountered the issue rarely, now. The countdown starts when you open the print view.