I have this configuration: apache 2.4.6 on a centos 7, configured as https reverse proxy on a filesender server (http://filesender.org/), on a Redhat 5.3 server. Filesender is a software for sending big files with email links. The error occurs clicking on the download.php link (for downloading files), and only for very big files (several GB I guess). Direct links to filesender server work. Finally I found the problem, but don't know why it happens: I tought the problem could be in the headers sent by download.php, so I tryied to comment them one by one and I found that the one which gives error is the one which sends file dimension: header('Content-Length: '.$functions->getFileSize($file)); Commenting out this one eliminates the error. I don't know if it occurs only with certain type of file or in https only. Here is verbose log: [Tue May 14 12:09:09.995372 2019] [ssl:debug] [pid 5421] ssl_engine_kernel.c(224): [client xxx.xxx.xxx.xxx:14019] AH02034: Initial (No.1) HTTPS request received for child 32 (server yyy.yyy.yyy.yyy:443) [Tue May 14 12:09:09.995577 2019] [authz_core:debug] [pid 5421] mod_authz_core.c(835): [client xxx.xxx.xxx.xxx:14019] AH01628: authorization result: granted (no directives) [Tue May 14 12:09:09.995915 2019] [proxy:debug] [pid 5421] mod_proxy.c(1117): [client xxx.xxx.xxx.xxx:14019] AH01143: Running scheme http handler (attempt 0) [Tue May 14 12:09:09.995947 2019] [proxy_ajp:debug] [pid 5421] mod_proxy_ajp.c(713): [client xxx.xxx.xxx.xxx:14019] AH00894: declining URL http://yyy.yyy.yyy.yyy/filesender/download1.php?vid=zzz [Tue May 14 12:09:09.995980 2019] [proxy_fcgi:debug] [pid 5421] mod_proxy_fcgi.c(963): [client xxx.xxx.xxx.xxx:14019] AH01076: url: http://yyy.yyy.yyy.yyy/filesender/download1.php?vid=zzz proxyname: (null) proxyport: 0 [Tue May 14 12:09:09.995990 2019] [proxy_fcgi:debug] [pid 5421] mod_proxy_fcgi.c(966): [client xxx.xxx.xxx.xxx:14019] AH01077: declining URL http://yyy.yyy.yyy.yyy/filesender/download1.php?vid=zzz [Tue May 14 12:09:09.996020 2019] [proxy:debug] [pid 5421] proxy_util.c(2256): [client xxx.xxx.xxx.xxx:14019] AH00944: connecting http://yyy.yyy.yyy.yyy/filesender/download1.php?vid=zzz to yyy.yyy.yyy.yyy:80 [Tue May 14 12:09:09.996453 2019] [proxy:debug] [pid 5421] proxy_util.c(2422): [client xxx.xxx.xxx.xxx:14019] AH00947: connected /filesender/download1.php?vid=zzz to yyy.yyy.yyy.yyy:80 [Tue May 14 12:09:10.708571 2019] [proxy_http:error] [pid 5421] (104)Connection reset by peer: [client xxx.xxx.xxx.xxx:14019] AH01102: error reading status line from remote server yyy.yyy.yyy.yyy:80 [Tue May 14 12:09:10.708731 2019] [proxy_http:debug] [pid 5421] mod_proxy_http.c(1363): [client xxx.xxx.xxx.xxx:14019] AH01105: NOT Closing connection to client although reading from backend server yyy.yyy.yyy.yyy:80 failed. [Tue May 14 12:09:10.708801 2019] [proxy:error] [pid 5421] [client xxx.xxx.xxx.xxx:14019] AH00898: Error reading from remote server returned by /filesender/download1.php [Tue May 14 12:09:15.715088 2019] [ssl:debug] [pid 5421] ssl_engine_io.c(992): [client xxx.xxx.xxx.xxx:14019] AH02001: Connection closed to child 32 with standard shutdown (server yyy.yyy.yyy.yyy:443) Here is proxy vhost: <VirtualHost xxx.xxx.xxx.xxx:443> ServerName yyy.yyy.yyy.yyy:443 ErrorLog logs/filesender_ssl_error_log TransferLog logs/filesender_ssl_access_log LogLevel debug ProxyPass / http://yyy.yyy.yyy.yyy/ ProxyPassReverse / http://yyy.yyy.yyy.yyy/ SSLEngine on SSLProtocol +TLSv1.2 SSLCipherSuite ALL:!ADH:!EXPORT:!SSLv2:!RC4:!DES-CBC-SHA:!EDH-RSA-DES-CBC-SHA:!AECDH-DES-CBC3-SHA:!AECDH-AES128-SHA:!AECDH-AES256-SHA:RC4+RSA:+HIGH:+MEDIUM:+LOW:!3DES:!IDEA SSLCertificateFile /etc/pki/tls/certs/yyy.yyy.yyy.yyy.cer SSLCertificateKeyFile /etc/pki/tls/private/yyy.yyy.yyy.yyy.key SSLCertificateChainFile /etc/pki/tls/certs/yyy.yyy.yyy.yyy.cer CustomLog logs/filesender_ssl_request_log \ "%t %h %{SSL_PROTOCOL}x %{SSL_CIPHER}x \"%r\" %b" </VirtualHost> These are headers sent by backend server: Date: Tue, 14 May 2019 10:37:55 GMT Server: Apache/2.2.3 (Red Hat) X-Powered-By: PHP/5.3.3 Cache-Control: private, max-age=10800, pre-check=10800 Last-Modified: Tue, 14 May 2019 10:01:03 GMT Content-Length: 5165363650 Content-Disposition: attachment; filename="yyy.7z" Connection: close Content-Type: application/octet-stream With these headers I got error, if I remove Content-Length header I can download file.