Flask Socket IO return status 400 When deploy to Server - python-3.x

Question

I using flask socket io to implementing the notification to my multiple clients using my application.
The flask socket is working well on my local development but the problem happen I deployed it to use on the server. It most of the time returned status 400 frequently and down the server sometime. I tried digging into source to root cause but I could not.
Below is a snippet that I had a problem:
Here is an init file for initializing application
from __future__ import absolute_import
import os
import redis
import flask_sqlalchemy as sa
from flask import Flask
from flask_socketio import SocketIO
from flask_cors import CORS
from .core.constant import MKT_BLUEPRINT, admin
# Initialize the core application and configure the app
app = Flask(__name__, instance_relative_config=True)
CORS(app)
# Initialize the core application and configure the app
app.config.from_object('mkt.config')
# redis address: "redis://localhost:6379/0"
redis_add = "redis://localhost:6379/0"
async_mode = None
notify_socketio = SocketIO(app, cors_allowed_origins="*",
message_queue=redis_add,
async_mode=async_mode
)
db = sa.SQLAlchemy(app)
app.register_blueprint(admin, url_prefix='/%s'%MKT_BLUEPRINT)
And then on client side, I use this js script
$(document).ready(function() {
var domain = "{{notify_domain|safe}}"
var socket = io(domain);
socket.on('connect', function() {
var user = "{{user|safe}}"
console.log("im in connect", user)
socket.emit('join_room', {room: user});
});
});
Then on server I config the nginx as below:
server {
listen 443 ssl;
server_name xxx;
include /config/nginx/ssl.conf;
location / {
proxy_read_timeout 300s;
proxy_connect_timeout 300s;
proxy_send_timeout 300s;
proxy_pass http://xxx:8000;
}
location /socket.io {
proxy_set_header Host $http_host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
proxy_set_header Access-Control-Allow-Origin *;
proxy_http_version 1.1;
proxy_buffering off;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "Upgrade";
proxy_pass http://xxx:8000/socket.io;
}
}
And here are dependencies that I'm using in my application:
#for notification to client
Flask-SocketIO==5.1.1
#for notification to client
Flask-SocketIO==5.1.1
python-engineio==4.2.1
python-socketio==5.4.0
Without any misconfiguration, I logged in console and below
Till now I still could not know what caused this error 400 (bad request) and solved it. Please kindly help. Thank so much.