使用 nginx 代理的 websocket 经常会出现消息延迟的现象，请问可能是什么原因？

个人的 nginx 配置如下：

upstream websocket {
    server 127.0.0.1:10300;
    server 127.0.0.1:10301;
    server 127.0.0.1:10302;
  }


server {
    listen 80;
    client_max_body_size 4G;
    access_log /home/work/logs/nginx_access.log;
    error_log /home/work/logs/nginx_error.log;
    # 域名
    server_name www.example.com;

   add_header X-UA-Compatible "IE=edge,chrome=1"; # IE 用最新内核渲染页面

   location / {
        proxy_pass http://websocket;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "Upgrade";

        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header Host $http_host;
        proxy_set_header X-NginX-Proxy true;
        proxy_redirect default;
        add_header "Access-Control-Allow-Origin" "*";
        add_header "Access-Control-Allow-Credentials" "true";
        add_header "Access-Control-Allow-Headers" "X-Requested-With";
        }
  }