Dear Jorge,
Thanks for your clarification and updates.
After investigation, I'd like to confirm whether the students are using the free version of the Teams applications on their computers. If yes, there may be some log-in issues in the free version of the Teams application. We have a specific channel coping
with the free version of the Teams application related issues. I suggest you let them post a new thread here
for further help.
If their Teams applications aren't the free versions and they are using the older versions of the Teams applications,
Microsoft has temporarily suspended blocking users from signing-in to the Teams applications due to the current situation with Coronavirus COVID-19. As you are the IT administrator, you
can use the Teams update policies in the Teams admin center to control the automatic update of their Teams applications to see if they can log into the Teams applications.
Meanwhile, I suggest you let them log into the web version of Microsoft Teams to see if they can move forward as well.
If the Teams applications aren't free versions and are in the latest version, I'm afraid that there may be some issues in the students' accounts themselves. I kindly suggest you
follow the steps in the article to open a
support ticket to our related team to fix the account issues from backend.
Sorry for that our category may have limited resources on fixing the account issues from backend.
Thanks for your understanding.
Cliff