We are currently working on 3 courses. The course with the problem is the course with ID 23. The unit named 'Social Media' is only showing two pages. It should have the following:
Social Media Overview
I've looked in the WP database and I can see the 'missing' posts in there. They have the correct parent ID (36) and I can't see any other reason that they aren't displaying under the relevant unit.
We had this happen a few months ago and in that case the parent IDs had been set to '0'. This time it's obviously a different problem. I have granted support access via the WPMUDev dashboard.