Additional file-related features and issues within Microsoft Teams for business
Hi Meghan,
Sorry for the trouble caused at your end.
From the description provided, seems like the three students have lost access to the Class Materials folder in the Class type team. We assume this problem could be caused due to Unique permissions to the Class Material Document Library in the related SharePoint team site. Whenever you create a Microsoft Team, it creates a SharePoint team site with the respective team. So, the beginning step, to look at this problem is to check the permission of those Class Materials Document Library. Follow the below steps:
Open the Microsoft Teams> Go to Class where the assignment is submitted> General tab> Click on three dots beside the Team> Open in SharePoint> Site Contents in the Navigation bar> Class Materials> Settings (Gear icon)> Library settings> Permissions for this document library> Check permission> Enter the student's name and check.
If the permission level is none, it means those students can't see those folders. In this case, you need to Grant permissions to them again.
So, please give a try by following the above steps and let us know the result.
Best Regards,
Chitrahaas