Nginx reverse proxy net::ERR_HTTP2_PROTOCOL_ERROR - nginx

Question

I have a Java (Micronaut) + Vue.js application that is running on port 8081. The app is accessed through a nginx reverse proxy that also uses a SSL certificate from Letsencrypt. Everything seems to work fine except for file uploads in the app. If a small file is being uploaded maybe < 1MB then everything works fine. If a larger file is being uploaded then the file upload request fails and in Chrome console net::ERR_HTTP2_PROTOCOL_ERROR is shown. If I send the large file upload request with some tool like Postman then the response status is shown to bee 200 OK, but the file has still not been uploaded and the response sent back from the server seems to be partial.
If I skip the nginx proxy and access the API on port 8081 directly then also the larger files can be uploaded.
Nginx error log show that the upload request timed out.
2021/06/07 20:45:20 [error] 32801#32801: *21 upstream timed out (110: Connection timed out) while reading upstream, client: XXX, server: XXX, request: "POST XXX HTTP/2.0", upstream: "XXX", host: "XXX", referrer: "XXX"
I have similar setups with nginx working for other apps and there all file uploads are working as expected. But in this case I am not able to figure out why the net::ERR_HTTP2_PROTOCOL_ERROR occurs. I have tried many suggestions that I could find from the internet but none seem to work in this case.
I have verified that there is enough space on the server to upload the files. Setting proxy_max_temp_file_size 0; as suggested here did not have any effect. Increasing http2_max_field_size and http2_max_header_size or large_client_header_buffers as suggested here did not work.
My global nginx configuration looks like this:
user www-data;
worker_processes auto;
pid /run/nginx.pid;
include /etc/nginx/modules-enabled/*.conf;
events {
worker_connections 768;
# multi_accept on;
}
http {
##
# Basic Settings
##
sendfile on;
tcp_nopush on;
tcp_nodelay on;
keepalive_timeout 65;
types_hash_max_size 2048;
server_tokens off;
include /etc/nginx/mime.types;
default_type application/octet-stream;
##
# SSL Settings
##
ssl_protocols TLSv1 TLSv1.1 TLSv1.2 TLSv1.3; # Dropping SSLv3, ref: POODLE
ssl_prefer_server_ciphers on;
##
# Logging Settings
##
access_log /var/log/nginx/access.log;
error_log /var/log/nginx/error.log;
##
# Gzip Settings
##
gzip on;
##
# Virtual Host Configs
##
include /etc/nginx/conf.d/*.conf;
include /etc/nginx/sites-enabled/*;
}
Nginx configuration for the specific host looks like this:
server {
server_name XXX;
client_max_body_size 100M;
location / {
proxy_set_header Host $host;
proxy_set_header X-Forwarded-For $remote_addr;
proxy_set_header X-Forwarded-Proto https;
proxy_pass http://XXX:8081;
}
listen 443 ssl; # managed by Certbot
ssl_certificate /etc/letsencrypt/live/XXX/fullchain.pem; # managed by Certbot
ssl_certificate_key /etc/letsencrypt/live/XXX/privkey.pem; # managed by Certbot
include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot
}
server {
if ($host = XXX) {
return 301 https://$host$request_uri;
} # managed by Certbot
if ($host = XXX) {
return 301 https://$host$request_uri;
} # managed by Certbot
listen 80;
server_name XXX;
return 404; # managed by Certbot
}