Connection timeout from work, working anywhere else

[GuiPoM]

Hello,

nginx is the HTTP server that is provided with my home automation software,
jeedom. It is installed on my Raspberry Pi2.
Everyting is working fine, I can connect from my internal network and from
outside.

But, when connecting from work, I get an error (navigator displays and
certificate issue ...). 

I had a lool to the logs and here is the corresponding entry in
/usr/share/nginx/www/jeedom/log/nginx.error:
2015/04/16 18:38:27 [error] 2151#0: *38577 upstream timed out (110:
Connection timed out) while reading upstream, client: 109.99.99.99, server:
, request: "GET
/socket.io/?EIO=3&transport=websocket&sid=qY83EqT2TTpBpiTzAAIn HTTP/1.1",
upstream:
"http://127.0.0.1:8070/socket.io/?EIO=3&transport=websocket&sid=qY83EqT2TTpBpiTzAAIn",
host: "truc:4321"
2015/04/16 18:42:05 [error] 2150#0: *39108 upstream prematurely closed
connection while reading response header from upstream, client:
109.99.99.99, server: , request: "GET
/socket.io/?EIO=3&transport=polling&t=1429202405657-73&sid=lxHkscjGEw5l1p2YAAI8
HTTP/1.1", upstream:
"http://127.0.0.1:8070/socket.io/?EIO=3&transport=polling&t=1429202405657-73&sid=lxHkscjGEw5l1p2YAAI8",
host: "truc:4321", referrer:
"https://truc:4321/jeedom/index.php?v=d&p=history"

Of course 109.99.99.99 is my remote IP and "truc:4321" my domain name / port
!

I am not sure this only log may help, but many thanks if you were kind
enough to provide me some help to understand and fix my issue. I can do some
more tests and provide other logs, just let me know what I should do.

Thanks !

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,258187,258187#msg-258187