These classes are set to expire just before the next semester starts. If you are continuing your degree, you will be automatically re-enrolled and entered into the appropriate subject classes at the same time. There is nothing to worry about. If this date is incorrect, ask your supervisor to mail ss with the new due date, and your thesis class will be extended accordingly. The lecturer in charge of the subject will inform ss of the tutors, and the class will be added or extended to people's accounts accordingly.
Staff belong to a variety of classes.
Classes that aren't related to teaching a subject are generally extended for 2-3 years at a time. If all your classes are expiring together, then your account is about to expire and you will get a slightly different automatic message warning you of this. Otherwise, mail ss with a justification for extending your account.