From Timetable -> Timetable it is possible to view all the courses that have been planned.
If a course is not visible, it is advisable to wait for 5/10 minutes and then click on the F4 key of the keyboard to refresh the page.
If there are duplicates, it will be possible to delete one of the two as long as there are no enrolments. In that case, people should be moved from that course to another one and then it will be possible to delete the duplicate.