I have a joomla website and when I am trying to update a larger extension I get bad gateway (502) error.
I am able to update all small (normal) extensions.

I am getting this error in nginx error log: "upstream sent invalid status "-1 Copy failed" while reading response header from upstream"

I have checked the php-fpm log and there is nothing there connected to this particular error(I have it enabled in config).

All files and folders have www-data owner and proper permissions (I even tried with 777).

There are parts of nginx.conf that I tried editing to fix this issue but it didn't work:

http {

##
# Basic Settings
##
fastcgi_read_timeout 5m;
fastcgi_buffers 8 16k;
fastcgi_buffer_size 32k;
client_max_body_size 2M;
sendfile on;
tcp_nopush on;
tcp_nodelay on;
keepalive_timeout 6;
types_hash_max_size 2048;

...

CGI settings in sites-enabled conf:

# pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
#
location ~ \.php$ {
try_files $uri =404;
fastcgi_split_path_info ^(.+\.php)(/.+)$;
# NOTE: You should have "cgi.fix_pathinfo = 0;" in php.ini

# With php5-cgi alone:
#fastcgi_pass 127.0.0.1:9000;

# With php5-fpm:
fastcgi_pass unix:/var/run/php5-fpm.sock;
fastcgi_index index.php;
include fastcgi_params;
}

I have tried searching this problem everywhere and tried many suggested fixes but I am unable to fix this issue.

Interesting problem is that I think its connected to the file size which I am trying to update (its around 3MB only still but bigger than all successfully updated extensions). The file (tar.gz gets updated successfully I think but after its being extracted or updated the error jumps)

My php.ini max_upload_size is 20M