this simple conf file does not work – it always connect to one server only (using Windows version 1.26.1)

worker_processes 1;

events {
    worker_connections 768;
}

http {
    upstream myapp {
#        ip_hash;
#        hash $binary_remote_addr consistent;
        server localhost:4000;
        server localhost:4001;
    }

    server {
        listen 4444 ssl;
        server_name localhost;  
        ssl_certificate     pem.pem;
        ssl_certificate_key key.key;

        ssl_protocols       TLSv1.2 TLSv1.3;
        ssl_ciphers         'ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256';
        ssl_prefer_server_ciphers on;

        ssl_session_cache   shared:SSL:10m;
        ssl_session_timeout 10m;

        location / {
            proxy_pass http://myapp;
            proxy_set_header Host $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;
        }
    }
}

what can be the problem?
I tested it using server created on two different programming languages and it is same.
Thank you.