Unable to keep connection active with ListenWebSocket

Hello,

I have this error when I connect a websocket client (tried 3 different ones) :

2024-06-12 19:28:10,731 WARN [qtp293746312-1015] o.a.n.w.jetty.RoutingWebSocketListener Unhandled Error: Endpoint

org.apache.nifi.websocket.jetty.RoutingWebSocketListener : org.eclipse.jetty.websocket.api.exceptions.CloseException:

org.eclipse.jetty.websocket.core.exception.WebSocketException: RoutingWebSocketListener OPEN method error: null

I see connection successful on the client and then it gets disconnected immediately.

Client and server are on the same machine, url is ws://127.0.0.1:8000/test (or any hostname, port and path). I suspected a firewall issue but Python's websockets server is fine.

Thanks for your time.