The most common reason for a team to get blocked is because the membership has expired. If the coach has not renewed before the expiration date, the team will automatically become blocked. Once the renew process is finalized (i.e.: the renew process from the Classroom application) the team will become unblocked automatically.
However, some other times a team can become blocked from other reasons. Usually, when the team is blocked, a notification will appear on the screen which includes the reason.
If you ever have questions, feel free to contact us at firstname.lastname@example.org and we will clarify everything shortly.