Hello,
The duplicated courses are listed is the student courses list who bought the original course,
The good part that the student don't have access to these courses.
Regards
The X Learner
Try deleting the course meta and re-save the course. Course duplication should be done after the course creation, an already running course would result in duplication of meta as well which contain student information.
1. Go to WP Admin->LMS->All courses
2. Edit the course.
3. Enable "Custom fields" from screen options :
4. Locate the custom field (with numeric name/meta key)and delete :