RE the nginx config, I'd assume that it's related to the ws forwarding settings. Not hugely familiar with the intricacies of it all though.
RE JupyterHub,perhaps you want https://zero-to-jupyterhub.readthedocs.io/en/stable/resources/reference.html#hub-service-type or proxy-service-type?
service.beta.kubernetes.io/aws-load-balancer-backend-protocol: tcp, what would be helpful to debug too. I haven't needed to do that in the past with EKS.
I'm also very curious about what you mean by
Could not use Jupyterhub's built in IP whitelisting feature because jupyterhub no longer sees real external IP addresses.