Good evening,
I believe I can help you diagnose your nginx problem as it appears your Nginx server can't communicate with the origin or host node's serving content, this can be for a variety of reasons which I can asses and advise on.
Can you tell me if the servers have worked before or if this an issue that has been present from the start?
If you have any questions or comment's please don't hesitate to contact me.
Best regards
Chris