When you run NodeBB in a cloud that has a load-balancer, reverse proxy, routers etc., it has to be configured to work properly, especially when you scale the server to use multiple instances.
One of the constraints Socket.io, SockJS and similar libraries have is that they need to continuously talk to the same instance of the server. They work perfectly well when there is only 1 instance of the server
Found this post too
That pretty much explains the issue i'm encountering on Cloud Foundry. Suspect it will apply to AWS too ...