WebSocket proxy to Streamlit fails when using custom ports (8080/8443) in Nginx Proxy Manager

I deployed Nginx Proxy Manager using Docker:

services:
  app:
    image: jc21/nginx-proxy-manager:latest
    ports:
      - '81:81'
      - '80:80'
      - '443:443'
    restart: unless-stopped
    volumes:
      - /mnt/pool0/data/appdata/npm/data:/data
      - /mnt/pool0/data/appdata/npm/letsencrypt:/etc/letsencrypt

I configured it to proxy a Streamlit app running on port 8501 to the domain st.nas.lan.
WebSocket support is enabled, and I am using a wildcard certificate *.nas.lan.

With the default ports (80/443), everything works correctly:

• http://st.nas.lan/
• https://st.nas.lan/

Both the web app and WebSocket connections work as expected.

However, after changing the exposed ports to 8080 and 8443 (e.g. 8080:80 and 8443:443), I encounter issues:

• http://st.nas.lan:8080/ loads, but WebSocket fails:

  • ws://st.nas.lan:8080/_stcore/stream

• https://st.nas.lan:8443/ also fails:

  • wss://st.nas.lan:8443/_stcore/stream

The WebSocket connection cannot be established.

Question:
Is there any special configuration required in Nginx Proxy Manager when using non-standard ports (e.g. 8080/8443) for WebSocket proxying?

Or is this a limitation/known issue?

Any help would be appreciated.

Start by reproducing the Streamlit WebSocket failure with the shown Docker port mappings and the Nginx Proxy Manager proxy-host settings. Compare the working 80/443 setup with 8080/8443 and determine whether an available configuration fixes the connection or whether the behavior is a confirmed limitation.