Thx, @jwunderl!
I’ve forwarded your suggestions about iframe /cross origin to the IT department, but unable to check again on the student’s chromebooks until next week.
@richard: Did you get any useful data points you could share in this analog case with all required domains reachable, but the simulator still not loading?;
Wish you all a great weekend on the other west coast (already weekend here…)! 
Br,
Vegard