Nginx empty responses for an upstream, although the upstream is healthy - node.js

Question

So I have a node.js express app, and the backend seems very healthy, but nginx returns the correct status code, but no response, response is always empty
this is my configuration for a 3x upstreams using 3 different subdomains over SSL
##
# You should look at the following URL's in order to grasp a solid understanding
# of Nginx configuration files in order to fully unleash the power of Nginx.
# https://www.nginx.com/resources/wiki/start/
# https://www.nginx.com/resources/wiki/start/topics/tutorials/config_pitfalls/
# https://wiki.debian.org/Nginx/DirectoryStructure
#
# In most cases, administrators will remove this file from sites-enabled/ and
# leave it as reference inside of sites-available where it will continue to be
# updated by the nginx packaging team.
#
# This file will automatically load configuration files provided by other
# applications, such as Drupal or Wordpress. These applications will be made
# available underneath a path with that package name, such as /drupal8.
#
# Please see /usr/share/doc/nginx-doc/examples/ for more detailed examples.
##
upstream frontend {
server web:80;
}
upstream api {
server backend:4000;
}
upstream manage {
server admin:5000;
}
server {
# SSL configuration
#
# listen 443 ssl default_server;
# listen [::]:443 ssl default_server;
#
# Note: You should disable gzip for SSL traffic.
# See: https://bugs.debian.org/773332
#
# Read up on ssl_ciphers to ensure a secure configuration.
# See: https://bugs.debian.org/765782
#
# Self signed certs generated by the ssl-cert package
# Don't use them in a production server!
#
# include snippets/snakeoil.conf;
# root /var/www/html;
# Add index.php to the list if you are using PHP
# index index.html index.htm index.nginx-debian.html;
server_name example.com test.example.com api-test.example.com www.example.com manage-test.example.com; # managed by Certbot
# if ($subdomain = '') {
# return 301 https://www.example.com$request_uri;
# }
set $upstreamed "frontend";
if ($host = 'api-test.example.com') {
set $upstreamed "api";
}
if ($host = 'api-manage.example.com') {
set $upstreamed "manage";
}
location / {
if ($request_method = 'OPTIONS') {
add_header 'Access-Control-Allow-Origin' '*' 'always';
add_header 'Access-Control-Allow-Methods' 'GET, POST, PUT, PATCH, DELETE, OPTIONS' 'always';
#
# Custom headers and headers various browsers *should* be OK with but aren't
#
add_header 'Access-Control-Allow-Headers' 'Authorization,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range';
#
# Tell client that this pre-flight info is valid for 20 days
#
add_header 'Access-Control-Max-Age' 1728000;
add_header 'Content-Type' 'text/plain; charset=utf-8';
add_header 'Content-Length' 0;
return 204;
}
if ($request_method = 'POST') {
add_header 'Access-Control-Allow-Origin' '*' 'always';
add_header 'Access-Control-Allow-Methods' 'GET, POST, PUT, PATCH, DELETE, OPTIONS' 'always';
add_header 'Access-Control-Allow-Headers' 'Authorization,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range' 'always';
add_header 'Access-Control-Expose-Headers' 'Content-Length,Content-Range' 'always';
}
if ($request_method = 'GET') {
add_header 'Access-Control-Allow-Origin' '*' 'always';
add_header 'Access-Control-Allow-Methods' 'GET, POST, PUT, PATCH, DELETE, OPTIONS' 'always';
add_header 'Access-Control-Allow-Headers' 'Authorization,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range' 'always';
add_header 'Access-Control-Expose-Headers' 'Content-Length,Content-Range' 'always';
}
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection 'upgrade';
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_redirect off;
proxy_buffering off;
proxy_pass http://$upstreamed;
}
listen [::]:443 ssl ipv6only=on; # managed by Certbot
listen 443 ssl; # managed by Certbot
ssl_certificate /etc/letsencrypt/live/test.example.com/fullchain.pem; # managed by Certbot
ssl_certificate_key /etc/letsencrypt/live/test.example.com/privkey.pem; # managed by Certbot
include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot
}
server {
if ($host = manage.test.example.com) {
return 301 https://$host$request_uri;
} # managed by Certbot
if ($host = api-test.example.com) {
return 301 https://$host$request_uri;
} # managed by Certbot
if ($host = test.example.com) {
return 301 https://$host$request_uri;
} # managed by Certbot
if ($host = www.example.com) {
return 301 https://$host$request_uri;
} # managed by Certbot
if ($host = example.com) {
return 301 https://www.$host$request_uri;
} # managed by Certbot
listen 80 ;
listen [::]:80 ;
server_name example.com test.example.com api-test.example.com www.example.com manage-test.example.com;
return 404; # managed by Certbot
}