[Python] Python Socketio client has a transport error by connection with Flask-SocketIO-Server...

I want to connect my Raspberry Pi 5 whit a python-socketio client to connect whit my Flask-SocketIO server on a different device. I'm using a nginx as a WebSocket Reverse Proxy. My Problem is that i got regularly "transport error" and the client disconnected, without me doing anything or there being any connection problems. I checked the internet connection but I couldn't find any connection problems and could not detect any difference between a LAN and WLAN connection. The strange thing is, that when i use the same Code on my Windows PC it worked whitout a Problem. The Server was befor added the connect to my Raspberry Pi 5 only for iOS Apps and it worked also well. What could be the problem or what can I do to better identify the problem?

Here is the Error on my Raspberry Pi 5:

Received packet PING data
[INFO ] Received packet PING data
Sending packet PONG data
[INFO ] Sending packet PONG data
WebSocket connection was closed, aborting
[WARNING] WebSocket connection was closed, aborting
Waiting for write loop task to end
[INFO ] Waiting for write loop task to end
Exiting write loop task
[INFO ] Exiting write loop task
Engine.IO connection dropped
[INFO ] Engine.IO connection dropped
[DISCONNECT]: reason: transport error
[DEBUG]: "transport error"
Connection failed, new attempt in 3.30 seconds
Exiting read loop task
[INFO ] Connection failed, new attempt in 3.30 seconds
[INFO ] Exiting read loop task
Attempting WebSocket connection to wss://www.mylink.de/socket.io/?transport=websocket&EIO=4
[INFO ] [Attempting WebSocket connection to wss]//www.mylink.de/socket.io/?transport=websocket&EIO=4
WebSocket connection accepted with {'sid': 'dGtmnqUR9rU279m1AAAU', 'upgrades': [], 'pingTimeout': 20000, 'pingInterval': 25000, 'maxPayload': 1000000}
[INFO ] [WebSocket connection accepted with {'sid'] 'dGtmnqUR9rU279m1AAAU', 'upgrades': [], 'pingTimeout': 20000, 'pingInterval': 25000, 'maxPayload': 1000000}
Engine.IO connection established
[INFO ] Engine.IO connection established
Sending packet MESSAGE data 0{}
[INFO ] Sending packet MESSAGE data 0{}
Received packet MESSAGE data 0{"sid":"sVrC7eaUscRr558dAAAV"}
[INFO ] Received packet MESSAGE data 0{"sid":"sVrC7eaUscRr558dAAAV"}
Namespace / is connected
[INFO ] Namespace / is connected
[INFO]: Verbunden mit dem Server.
Emitting event "test" [/]
[INFO ] Emitting event "test" [/]
Sending packet MESSAGE data 2["test",{"Hallo":"World"}]
[INFO ] Sending packet MESSAGE data 2["test",{"Hallo":"World"}]
Reconnection successful
[INFO ] Reconnection successful


Here is the Error on my Server:

dkoIY3aUHWE7_HlkAAAS: Sending packet PING data None
dkoIY3aUHWE7_HlkAAAS: Received packet PONG data
dkoIY3aUHWE7_HlkAAAS: Sending packet PING data None
dkoIY3aUHWE7_HlkAAAS: Received packet PONG data
--------------------------------------------------------------------------------
[DISCONNECT]reason = transport close
[DISCONNECT] - traceback: NoneType: None
--------------------------------------------------------------------------------
dGtmnqUR9rU279m1AAAU: Sending packet OPEN data {'sid': 'dGtmnqUR9rU279m1AAAU', 'upgrades': [], 'pingTimeout': 20000, 'pingInterval': 25000, 'maxPayload': 1000000}
dGtmnqUR9rU279m1AAAU: Received request to upgrade to websocket
dGtmnqUR9rU279m1AAAU: Upgrade to websocket successful
dGtmnqUR9rU279m1AAAU: Received packet MESSAGE data 0{}
dGtmnqUR9rU279m1AAAU: Sending packet MESSAGE data 0{"sid":"sVrC7eaUscRr558dAAAV"}
Ein Client hat sich verbunden.
dGtmnqUR9rU279m1AAAU: Received packet MESSAGE data 2["test",{"Hallo":"World"}]
received event "test" from sVrC7eaUscRr558dAAAV [/]
dGtmnqUR9rU279m1AAAU: Sending packet PING data None
dGtmnqUR9rU279m1AAAU: Received packet PONG data
dGtmnqUR9rU279m1AAAU: Sending packet PING data None
dGtmnqUR9rU279m1AAAU: Received packet PONG data
dGtmnqUR9rU279m1AAAU: Sending packet PING data None
--------------------------------------------------------------------------------
[DISCONNECT]reason = transport close
[DISCONNECT] - traceback: NoneType: None

--------------------------------------------------------------------------------
dGtmnqUR9rU279m1AAAU: Received packet PONG data
gNo1jQEFB1pggf7-AAAW: Sending packet OPEN data {'sid': 'gNo1jQEFB1pggf7-AAAW', 'upgrades': [], 'pingTimeout': 20000, 'pingInterval': 25000, 'maxPayload': 1000000}
gNo1jQEFB1pggf7-AAAW: Received request to upgrade to websocket
gNo1jQEFB1pggf7-AAAW: Upgrade to websocket successful
gNo1jQEFB1pggf7-AAAW: Received packet MESSAGE data 0{}
gNo1jQEFB1pggf7-AAAW: Sending packet MESSAGE data 0{"sid":"p2sePiDTxpxpymyQAAAX"}
Ein Client hat sich verbunden.
gNo1jQEFB1pggf7-AAAW: Received packet MESSAGE data 2["test",{"Hallo":"World"}]
received event "test" from p2sePiDTxpxpymyQAAAX [/]
gNo1jQEFB1pggf7-AAAW: Sending packet PING data None
gNo1jQEFB1pggf7-AAAW: Received packet PONG data


First I have checked and updated the Version from Flask and flask_socketio on my server and on my client from python-socketio[client], then i have reduced the code of the server and client to a "connect" and "disconnect" function. Here is the Code from my client:

def run_socketio_client(self):
client = SocketIOClient()
client.connect("https://www.mylink.de") # Server-URL
client.wait()


import socketio

class SocketIOClient:
def __init__(self):
self.sio = socketio.Client(
reconnection=True,
reconnection_delay=3,
reconnection_delay_max=10,
logger=True,
engineio_logger=True
)

# Events registrieren
self.sio.on('connect', self.on_connect)
self.sio.on('disconnect', self.on_disconnect)

def on_connect(self):
print("[INFO]: Verbunden mit dem Server.")
self.sio.emit("test", {"Hallo": "World"})

def on_disconnect(self, reason=None):
print("[DISCONNECT]: reason:", reason)

if reason == self.sio.reason.CLIENT_DISCONNECT:
print("[DEBUG]: CLIENT_DISCONNECT")
elif reason == self.sio.reason.SERVER_DISCONNECT:
print("[DEBUG]: SERVER_DISCONNECT")
elif reason == self.sio.reason.TRANSPORT_ERROR:
print("[DEBUG]: \"transport error\"")
else:
print('[DEBUG]: other reason:', reason)

def connect(self, url):
print("[INFO]: Verbindungsaufbau mit dem Server...")
self.sio.connect(
url,
transports=['websocket'],
wait_timeout=10,
retry=True
)

def wait(self):
self.sio.wait()


and here from my server:

from flask import Flask, request
from flask_socketio import SocketIO, emit, join_room, leave_room, close_room, rooms, disconnect
import traceback

app = Flask(__name__)
socketio = SocketIO(app,
server=True,
logger=True,
engineio_logger=True,
cors_allowed_origins="*",
async_mode="gevent",
transports=["websocket"])

@socketio.on_error_default
def handle_error(e):
print(f"[ERROR] - error: {e}")
print("[ERROR] - handle_error traceback:")
print(traceback.format_exc())

# WebSocket: Verbindung hergestellt
@socketio.on('connect')
def handle_connect():
print('Ein Client hat sich verbunden.')

@socketio.on('disconnect')
def disconnect(reason=None):
#sid = request.sid
print("------------------------------------------------------------------------------")
print("[DISCONNECT]reason =", reason)
print("[DISCONNECT] - traceback:", traceback.format_exc())
print("------------------------------------------------------------------------------")


if __name__ == '__main__':
socketio.run(app, port=5000)


Unfortunately the Raspberry still has regularly a transport error and my Windows program with the same code doesn't.

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