I may have identified a potential bug.
On our installation if the last unit does not have a question instead of issuing an email with a certificate link it presents a pre-completion message.
That is: It indicates that the student has successfully completed the course and it will be assessed by the instructor/teacher.
To confirm a unit with no question works fine as long as it isn't the last unit.
I instigated a live chat with one of your colleagues over the weekend and they confirmed they can replicate.
I agreed with them to set up a staging site just with CoursePress Pro installed so I can eliminate an plugin conflict.
Not sure if you wish to report to the developers before I test or wait until I confirm.