First, the users were assigned to the course with an Instructor role.
Instructors can view and complete the courses in order to complete tests however, their progress is not recorded.
You can solve this by changing the user's role to the course from Instructor to Learner (1).
Second, you have shared the course with an unregistered user.
Users that access a shared course through the public URL, do not show up under the reporting features,. If the user does not register or sign up at the end of their log in, the system can not identify the users that have completed the course.
In case you have shared a course accidentally, you can solve this issue by simply un-sharing (1) the course. Users will now be obligated to log in to access its content.