Did you assign the students to the entire CSD class when you created the class or to a collection of lessons or to an individual unit?
If you assigned them to the entire CSD course or to a collection that has both units 2 and 3 in it, it should work as it has in the past, but if you somehow assigned them to a module that only includes one of the units in it, they may be working in a “different version” of the lessons than the one that is on your dashboard.
If you look closely at the URL’s of the two lessons, you should see them to be mostly the same, but if you see a difference (again see the post above), the students are probably working in a different version of the course.
This is an issue that the engineers are aware of and are hoping to find a fix for, but has of yet have not.
The solution is to make sure the students are in the same version and that you have assigned a class that includes both units. If not, you would have to assign the one that they are working in now and have a separate gradebook.
Now, this may not be your issue, but it’s the first thing that comes to mind and the first place I would check . If it’s not that, check back in and/or reach out to support@code.org so they can look closer at it because if it’s a gradebook issue, they would need internal access to diagnose it.
Hope this helps a little.
Mike