Upload of huge files

[ZTHawk]

Hi, I have an issue (again) to upload big files. Config:

map $http_upgrade $connection_upgrade {
    default upgrade;
    '' close;
}
upstream srvupstream {
    keepalive 32;
    keepalive_timeout 600s;
    server 10.12.34.56:443;
}
server {
    listen 443 ssl http2;
    listen [::]:443 ssl http2;
    server_name srv.mylocaldomain.com;
    ssl_certificate srv.pem;
    ssl_certificate_key srv.key;
    location / {
        proxy_request_buffering off;
        proxy_connect_timeout 600s;
        proxy_send_timeout 600s;
        proxy_read_timeout 600s;
        send_timeout 600s;
        client_max_body_size 500m;

        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection $connection_upgrade;
        proxy_redirect off;
        add_header X-Served-By $host;
        proxy_set_header Host $host;
        proxy_set_header X-Forwarded-Scheme $scheme;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-Host $host;
        proxy_set_header X-Forwarded-Port $server_port;
        proxy_set_header X-Forwarded-Server $host;
        proxy_pass https://srvupstream$request_uri;
        proxy_cache_bypass $http_upgrade;
    }
}

I can upload files that have ~10MB. But I cannot upload files ~350MB. According to my settings it should be possible to upload 500MB.
When I connect directly via IP then uploads are no issue. So it must be related to nginx/nginx-UI.

Anyone know how to fix it?