Complete Button not showing, Access Denied

A few weeks ago some of my students started having trouble with their course. The “Complete” button was missing from a few of the lessons and they were unable to click complete to get their certificate.

Additionally, one student was given an “access denied” message when she tried to click “finish course” with the lessons not yet completed. This happened even though I set my “pass grade” to 70% so she theoretically should not have to complete each lesson.

Can you please advise how to fix the missing “Complete lesson” button?

Also curious if there is a plugin where I could manually go in and change lessons to completed.

The page I need help with: [log in to see the link]