We are currently experiencing an outage that may block Classroom lab users from connecting to their virtual machines.
Issue:
If you have any classroom labs that were created on or before September 10, 2018, you may see that your lab users cannot connect to their virtual machines in your lab. Your lab users will see an error message on their virtual machines that says: "Error: Object reference not set to an instance of an object."
Resolution:
There is no workaround for this issue. We currently have a fix ready that is getting tested. We are trying to ship the fix by today. I will keep posting updates on the resolution here.
Thank you!