Javascript exception when navigating back to a page containing a user tour

I sometimes get a Type Error when I perform the following steps on the qa.moodledemo.net site using Chrome 98.0.... on Windows:

1. Login as a Teacher
2. Go to the My courses page. (https://qa.moodledemo.net/my/courses.php)
3. Click on any course.
4. Click on the browser's Back button.

I get the following error message:

When it happens, I can reproduce it easily and consistently. However, I have not quite figured out the sequence of events to reproduce it when it is not happening the rest of the time.

Just reporting this in case someone else can add to the details or might have an idea of why this happens.