iTunes U course on iPad/iPhone missing materials

An iTunes U course on my iPad and iPhone won't show all the available materials. Specifically, it is missing all the video and audio lectures except for the first ones. If I use my Mac everything is ok, and it is also on another iPad (with another App Store account) I borrowed. I tried un-enrolling and rejoining the course, uninstalling and reinstalling iTunes U, restoring the iPad but nothing worked.

Here is a view of the course from my iPad:

And here with all the materials as seen on another iPad:

I have no clue about what might be the problem, it seems so weird...