Hello all.
I have topology as follows:
client->NGINX->haproxy-> 4xapache servers.

Problem is, that on one page, we have option to download file - it is done through changing header. Resulting header is as follows:
Content-type: application/txt
Content-Length: "xxxxx"
Content-Disposition: attachment; filename="aaa.txt"

I'm getting 502 Bad Gateway, The server returned an invalid or incomplete response error everytime after clicking on link. In logs, there is nothing weird. When trying it directly through HAPROXY or directly through nginx (pointed to one of that apache servers) it is working correctly.

Do you have any idea about how to resolve it? Have anybody experienced something like this?
Many thanks for any reply concerning this.