Maybe this can help:
For start, you and your students should try to not perform the update all at once, to avoid depassing the maximum number allowed of open connections (at a time) from the same IP.
However, a banned IP is whitelisted after 24 hours, but you mentioned that the problem persists from more than one week:
Meanwhile I have checked your IP (I assume it’s the same one from which you accessed this forum, from Khon Kaen University), and it’s not in the banned IPs list.
Therefore, maybe there are other issues on your network.