JupyterHub running on corporate proxy

Our setup was, we installed JupyterHub (nginx as reverse proxy) on a AWS EC2 instance with a corporate proxy. Basically, we need to set this http_proxy= in order to access the internet. We’re able to install it and it was running properly until we discover this strange situation.

During our testing phase, we left a Jupyter window in a browser for a like 30mins-1hr. With cull-idle, the server will be killed, and we tried to logout > login.
Not particularly sure what’s the cause of this issue. But we receive this error Server user1 is slow to stop, then the jupyter hangsup for around 5mins+.