sio.save_session() raising KeyError: 'Session not found'

[PATAPOsha]

python-socketio==5.0.2
eventlet==0.30.0
Python 3.7.7 on linux (WSL2 Ubuntu 18.04.4 LTS)

I'm trying to run server from the docs using sessions.
My server code:

import socketio
import eventlet
from django.conf import settings

from mydjangoapp.wsgi import application

from chat_ws.logger import logger

# WS_CORS_ALLOWED_ORIGINS = ['http://127.0.0.1:8000', 'http://127.0.0.1:5000']
sio = socketio.Server(cors_allowed_origins=settings.WS_CORS_ALLOWED_ORIGINS, async_mode='eventlet')
app = socketio.WSGIApp(sio, application)

@sio.event(namespace='/chat')
def connect(sid, environ):
    print(f'connected: {sid}')
    sio.save_session(sid, {'username': 'test'}, namespace='/chat')

@sio.event(namespace='/chat')
def message(sid, data):
    print(f'message sid: {sid}')
    with sio.session(sid) as session:
        print(f"{session['username']} msg: {data}")
        sio.emit("message", "Zdarova!")

@sio.event(namespace='/chat')
def disconnect(sid):
    print('disconnect ', sid)

if __name__ == "__main__":
    eventlet.wsgi.server(eventlet.listen(("", 5000)), app)

My client code:

import time
import socketio

sio = socketio.Client()

@sio.on('connect', namespace='/chat')
def on_connect():
    print("I'm connected to the /chat namespace!")

@sio.on('join_event', namespace='/chat')
def on_message(data):
    print(f'[join_event]: {data}')

@sio.on('message', namespace='/chat')
def on_message(data):
    print(f'I received a message: {data}')

sio.connect('http://127.0.0.1:5000', namespaces=['/chat'])
time.sleep(5)
sio.emit('message', {'foo': 'bar'}, namespace='/chat')
print("sent msg.")

When client connects, server raises following error:

(25100) wsgi starting up on http://0.0.0.0:5000
(25100) accepted ('127.0.0.1', 60310)
127.0.0.1 - - [14/Dec/2020 13:07:17] "GET /socket.io/?EIO=4&transport=polling&t=NPXNBu7 HTTP/1.1" 200 329 0.001411
(25100) accepted ('127.0.0.1', 60312)
connected: jNJJ7jG2LFx5w5YRAAAB
message handler error
Traceback (most recent call last):
  File "/home/pata/.pyenv/versions/3.7.7/envs/env/lib/python3.7/site-packages/engineio/server.py", line 606, in _get_socket
    s = self.sockets[sid]
KeyError: 'Q2dEwhemB-8GAYSMAAAB'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "/home/pata/.pyenv/versions/3.7.7/envs/env/lib/python3.7/site-packages/engineio/server.py", line 595, in _trigger_event
    return self.handlers[event](*args)
  File "/home/pata/.pyenv/versions/3.7.7/envs/env/lib/python3.7/site-packages/socketio/server.py", line 722, in _handle_eio_message
    self._handle_connect(eio_sid, pkt.namespace)
  File "/home/pata/.pyenv/versions/3.7.7/envs/env/lib/python3.7/site-packages/socketio/server.py", line 622, in _handle_connect
    self.environ[eio_sid])
  File "/home/pata/.pyenv/versions/3.7.7/envs/env/lib/python3.7/site-packages/socketio/server.py", line 694, in _trigger_event
    return self.handlers[namespace][event](*args)
  File "/mnt/c/Users/pata/PycharmProjects/ec-3.0-backend/source/chat_ws/ws.py", line 65, in connect
    sio.save_session(sid, {'username': 'dgdfg'}, namespace='/chat')
  File "/home/pata/.pyenv/versions/3.7.7/envs/env/lib/python3.7/site-packages/socketio/server.py", line 459, in save_session
    eio_session = self.eio.get_session(sid)
  File "/home/pata/.pyenv/versions/3.7.7/envs/env/lib/python3.7/site-packages/engineio/server.py", line 231, in get_session
    socket = self._get_socket(sid)
  File "/home/pata/.pyenv/versions/3.7.7/envs/env/lib/python3.7/site-packages/engineio/server.py", line 608, in _get_socket
    raise KeyError('Session not found')
KeyError: 'Session not found'

Output log contains printed sid that was received inside connect() method: connected: jNJJ7jG2LFx5w5YRAAAB
I tried to look inside engineio/server.py Server._get_socket() method using debugger. There is one record inside self.sockets but it's completely different from what I'm printing inside my connect() method.

[miguelgrinberg]

The different sid values is a change introduced in the latest version of the Socket.IO protocol, that is expected. But this may be a bug introduced when I implemented this change.

[miguelgrinberg]

Fixed in release 5.0.3, please upgrade and let me know if you still experience problems.

[pavel-vorobyev]

Still experiencing this error on v5.0.4

[miguelgrinberg]

@pavel-vorobyev the issue reported in this bug is fixed. If you are receiving the same error, please open an issue and provide code that I can use to reproduce the error.