Provisional headers are shown (nginx proxy backend) how to fix?

Question

Nginx

Hi all!
I have a nodejs application that hangs on port 3000. Nginx hangs on port 80, which proxies a request to nodejs app. At the same time, proxying should be as transparent as possible, i.e. node, the application must receive the original client request with headers.
With this approach, I get some unpleasant result. The site is loading long and besides, I see a warning in the chrome console " provisional headers are shown ". Googling didn't work, please help

upstream backend {
    server 127.0.0.1:3000;
}

server {
        listen 80;
        server_name www.mydomain.com;
        return 301 $scheme://mydomain.com$request_uri;
}

server {
    listen 80;
    server_name mydomain.com;
    location / {
      proxy_set_header X-Real-IP $remote_addr;
      proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
      proxy_set_header Host $host;
      proxy_set_header X-NginX-Proxy true;

      proxy_pass http://backend;
      proxy_redirect off;
    }
 }