So it worked before, and now it doesn’t work. What makes you so absolutely sure that it must be a hosting issue, and could never be a problem on your network? Do you believe that hosting always changes for no reason but your school network never does?
Security blocklists are frequently updated with the latest information about identified threats. These list updates can also result in new false positives. If the issue is a network block on your end, then that’s why it worked before but doesn’t work now.