I know I'm late joining in on this, but am having a similar problem. I've tried playing with all the connection settings/bug detection settings as well as using a couple versions. WinSCP is on the list of allowed programs in Windows Firewall, FYI.
Here's the log for a failed connection attempt. Since it's prior to authentication, I assume it will work for your needs:
. 2015-07-24 08:28:23.858 --------------------------------------------------------------------------
. 2015-07-24 08:28:23.859 WinSCP Version 5.7.4 (Build 5553) (OS 6.1.7601 Service Pack 1 - Windows 7 Professional)
. 2015-07-24 08:28:23.859 Configuration: HKCU\Software\Martin Prikryl\WinSCP 2\
. 2015-07-24 08:28:23.859 Log level: Debug 2
. 2015-07-24 08:28:23.859 Local account: [removed]
. 2015-07-24 08:28:23.859 Working directory: C:\Program Files (x86)\WinSCP
. 2015-07-24 08:28:23.859 Process ID: 8068
. 2015-07-24 08:28:23.859 Command-line: "C:\Program Files (x86)\WinSCP\WinSCP.exe"
. 2015-07-24 08:28:23.859 Time zone: Current: GMT-6, Standard: GMT-7 (Mountain Standard Time), DST: GMT-6 (Mountain Daylight Time), DST Start: 3/8/2015, DST End: 11/1/2015
. 2015-07-24 08:28:23.859 Login time: Friday, July 24, 2015 8:28:23 AM
. 2015-07-24 08:28:23.859 --------------------------------------------------------------------------
. 2015-07-24 08:28:23.859 Session name: VMWare (Modified site)
. 2015-07-24 08:28:23.859 Host name: sftp2.eng.vmware.com (Port: 443)
. 2015-07-24 08:28:23.860 User name: [removed] (Password: Yes, Key file: No)
. 2015-07-24 08:28:23.860 Tunnel: No
. 2015-07-24 08:28:23.860 Transfer Protocol: SFTP (SCP)
. 2015-07-24 08:28:23.860 Ping type: N, Ping interval: 30 sec; Timeout: 15 sec
. 2015-07-24 08:28:23.860 Disable Nagle: No
. 2015-07-24 08:28:23.860 Proxy: none
. 2015-07-24 08:28:23.860 Send buffer: 0
. 2015-07-24 08:28:23.860 SSH protocol version: 2; Compression: Yes
. 2015-07-24 08:28:23.860 Bypass authentication: No
. 2015-07-24 08:28:23.860 Try agent: No; Agent forwarding: Yes; TIS/CryptoCard: No; KI: Yes; GSSAPI: Yes
. 2015-07-24 08:28:23.860 GSSAPI: Forwarding: No; Server realm:
. 2015-07-24 08:28:23.860 Ciphers: aes,blowfish,3des,WARN,arcfour,des; Ssh2DES: Yes
. 2015-07-24 08:28:23.860 KEX: dh-gex-sha1,dh-group14-sha1,dh-group1-sha1,rsa,WARN
. 2015-07-24 08:28:23.860 SSH Bugs: A,A,A,A,A,A,A,A,A,A,A
. 2015-07-24 08:28:23.860 Simple channel: No
. 2015-07-24 08:28:23.860 Return code variable: Autodetect; Lookup user groups: A
. 2015-07-24 08:28:23.860 Shell: default
. 2015-07-24 08:28:23.860 EOL: 0, UTF: 2
. 2015-07-24 08:28:23.860 Clear aliases: Yes, Unset nat.vars: Yes, Resolve symlinks: Yes
. 2015-07-24 08:28:23.860 LS: ls -la, Ign LS warn: Yes, Scp1 Comp: No
. 2015-07-24 08:28:23.860 SFTP Bugs: A,A
. 2015-07-24 08:28:23.860 SFTP Server: default
. 2015-07-24 08:28:23.860 Local directory: default, Remote directory: home, Update: Yes, Cache: Yes
. 2015-07-24 08:28:23.860 Cache directory changes: Yes, Permanent: Yes
. 2015-07-24 08:28:23.860 DST mode: 1
. 2015-07-24 08:28:23.860 --------------------------------------------------------------------------
. 2015-07-24 08:28:23.943 Looking up host "sftp2.eng.vmware.com"
. 2015-07-24 08:28:23.947 Connecting to 208.91.0.170 port 443
. 2015-07-24 08:28:23.950 Selecting events 63 for socket 972
. 2015-07-24 08:28:23.995 Waiting for the server to continue with the initialization
. 2015-07-24 08:28:23.995 Looking for incoming data
. 2015-07-24 08:28:23.995 Looking for network events
. 2015-07-24 08:28:23.995 Detected network event
. 2015-07-24 08:28:23.995 Enumerating network events for socket 972
. 2015-07-24 08:28:23.995 Enumerated 18 network events making 18 cumulative events for socket 972
. 2015-07-24 08:28:23.995 Handling network write event on socket 972 with error 0
. 2015-07-24 08:28:23.995 Handling network connect event on socket 972 with error 0
. 2015-07-24 08:28:23.995 Looking for network events
. 2015-07-24 08:28:38.997 Timeout waiting for network events
. 2015-07-24 08:28:38.997 Waiting for data timed out, asking user what to do.
. 2015-07-24 08:28:38.997 Asking user:
. 2015-07-24 08:28:38.997 **Host is not communicating for 15 seconds.
. 2015-07-24 08:28:38.997
. 2015-07-24 08:28:38.997 Wait for another 15 seconds?** ()
. 2015-07-24 08:28:39.512 Pooling for data in case they finally arrives
. 2015-07-24 08:28:39.512 Looking for network events
. 2015-07-24 08:28:39.512 Timeout waiting for network events
. 2015-07-24 08:28:40.028 Pooling for data in case they finally arrives
. 2015-07-24 08:28:40.028 Looking for network events
. 2015-07-24 08:28:40.028 Timeout waiting for network events
. 2015-07-24 08:28:40.541 Pooling for data in case they finally arrives
. 2015-07-24 08:28:40.541 Looking for network events
. 2015-07-24 08:28:40.542 Timeout waiting for network events
. 2015-07-24 08:28:41.056 Pooling for data in case they finally arrives
. 2015-07-24 08:28:41.056 Looking for network events
. 2015-07-24 08:28:41.056 Timeout waiting for network events
. 2015-07-24 08:28:41.560 Pooling for data in case they finally arrives
. 2015-07-24 08:28:41.560 Looking for network events
. 2015-07-24 08:28:41.560 Timeout waiting for network events
. 2015-07-24 08:28:42.070 Pooling for data in case they finally arrives
. 2015-07-24 08:28:42.070 Looking for network events
. 2015-07-24 08:28:42.070 Timeout waiting for network events
. 2015-07-24 08:28:42.574 Pooling for data in case they finally arrives
. 2015-07-24 08:28:42.574 Looking for network events
. 2015-07-24 08:28:42.574 Timeout waiting for network events
. 2015-07-24 08:28:43.084 Pooling for data in case they finally arrives
. 2015-07-24 08:28:43.084 Looking for network events
. 2015-07-24 08:28:43.084 Timeout waiting for network events
. 2015-07-24 08:28:43.587 Pooling for data in case they finally arrives
. 2015-07-24 08:28:43.587 Looking for network events
. 2015-07-24 08:28:43.587 Timeout waiting for network events
. 2015-07-24 08:28:44.098 Pooling for data in case they finally arrives
. 2015-07-24 08:28:44.098 Looking for network events
. 2015-07-24 08:28:44.098 Timeout waiting for network events
. 2015-07-24 08:28:44.598 Pooling for data in case they finally arrives
. 2015-07-24 08:28:44.598 Looking for network events
. 2015-07-24 08:28:44.598 Timeout waiting for network events
. 2015-07-24 08:28:45.114 Pooling for data in case they finally arrives
. 2015-07-24 08:28:45.114 Looking for network events
. 2015-07-24 08:28:45.114 Timeout waiting for network events
. 2015-07-24 08:28:45.616 Pooling for data in case they finally arrives
. 2015-07-24 08:28:45.616 Looking for network events
. 2015-07-24 08:28:45.616 Timeout waiting for network events
. 2015-07-24 08:28:46.127 Pooling for data in case they finally arrives
. 2015-07-24 08:28:46.127 Looking for network events
. 2015-07-24 08:28:46.127 Timeout waiting for network events
. 2015-07-24 08:28:46.633 Pooling for data in case they finally arrives
. 2015-07-24 08:28:46.633 Looking for network events
. 2015-07-24 08:28:46.633 Timeout waiting for network events
. 2015-07-24 08:28:47.141 Pooling for data in case they finally arrives
. 2015-07-24 08:28:47.141 Looking for network events
. 2015-07-24 08:28:47.141 Timeout waiting for network events
. 2015-07-24 08:28:47.644 Pooling for data in case they finally arrives
. 2015-07-24 08:28:47.644 Looking for network events
. 2015-07-24 08:28:47.644 Timeout waiting for network events
. 2015-07-24 08:28:48.156 Pooling for data in case they finally arrives
. 2015-07-24 08:28:48.156 Looking for network events
. 2015-07-24 08:28:48.156 Timeout waiting for network events
. 2015-07-24 08:28:48.669 Pooling for data in case they finally arrives
. 2015-07-24 08:28:48.669 Looking for network events
. 2015-07-24 08:28:48.669 Timeout waiting for network events
. 2015-07-24 08:28:49.169 Pooling for data in case they finally arrives
. 2015-07-24 08:28:49.169 Looking for network events
. 2015-07-24 08:28:49.169 Timeout waiting for network events
. 2015-07-24 08:28:49.683 Pooling for data in case they finally arrives
. 2015-07-24 08:28:49.683 Looking for network events
. 2015-07-24 08:28:49.683 Timeout waiting for network events
. 2015-07-24 08:28:50.183 Pooling for data in case they finally arrives
. 2015-07-24 08:28:50.184 Looking for network events
. 2015-07-24 08:28:50.184 Timeout waiting for network events
. 2015-07-24 08:28:50.697 Pooling for data in case they finally arrives
. 2015-07-24 08:28:50.697 Looking for network events
. 2015-07-24 08:28:50.697 Timeout waiting for network events
. 2015-07-24 08:28:51.197 Pooling for data in case they finally arrives
. 2015-07-24 08:28:51.197 Looking for network events
. 2015-07-24 08:28:51.197 Timeout waiting for network events
. 2015-07-24 08:28:51.711 Pooling for data in case they finally arrives
. 2015-07-24 08:28:51.711 Looking for network events
. 2015-07-24 08:28:51.711 Timeout waiting for network events
. 2015-07-24 08:28:52.211 Pooling for data in case they finally arrives
. 2015-07-24 08:28:52.211 Looking for network events
. 2015-07-24 08:28:52.211 Timeout waiting for network events
. 2015-07-24 08:28:52.725 Pooling for data in case they finally arrives
. 2015-07-24 08:28:52.725 Looking for network events
. 2015-07-24 08:28:52.725 Timeout waiting for network events
. 2015-07-24 08:28:53.225 Pooling for data in case they finally arrives
. 2015-07-24 08:28:53.225 Looking for network events
. 2015-07-24 08:28:53.225 Timeout waiting for network events
. 2015-07-24 08:28:53.739 Pooling for data in case they finally arrives
. 2015-07-24 08:28:53.739 Looking for network events
. 2015-07-24 08:28:53.739 Timeout waiting for network events
. 2015-07-24 08:28:54.239 Pooling for data in case they finally arrives
. 2015-07-24 08:28:54.239 Looking for network events
. 2015-07-24 08:28:54.239 Timeout waiting for network events
. 2015-07-24 08:28:54.753 Pooling for data in case they finally arrives
. 2015-07-24 08:28:54.753 Looking for network events
. 2015-07-24 08:28:54.753 Timeout waiting for network events
. 2015-07-24 08:28:55.254 Pooling for data in case they finally arrives
. 2015-07-24 08:28:55.254 Looking for network events
. 2015-07-24 08:28:55.254 Timeout waiting for network events
. 2015-07-24 08:28:55.768 Pooling for data in case they finally arrives
. 2015-07-24 08:28:55.768 Looking for network events
. 2015-07-24 08:28:55.768 Timeout waiting for network events
. 2015-07-24 08:28:56.269 Pooling for data in case they finally arrives
. 2015-07-24 08:28:56.269 Looking for network events
. 2015-07-24 08:28:56.269 Timeout waiting for network events
. 2015-07-24 08:28:56.782 Pooling for data in case they finally arrives
. 2015-07-24 08:28:56.782 Looking for network events
. 2015-07-24 08:28:56.782 Timeout waiting for network events
. 2015-07-24 08:28:57.282 Pooling for data in case they finally arrives
. 2015-07-24 08:28:57.282 Looking for network events
. 2015-07-24 08:28:57.282 Timeout waiting for network events
. 2015-07-24 08:28:57.500 Attempt to close connection due to fatal exception:
* 2015-07-24 08:28:57.500 **Terminated by user.**
. 2015-07-24 08:28:57.500 Closing connection.
. 2015-07-24 08:28:57.500 Sending special code: 12
. 2015-07-24 08:28:57.500 Selecting events 0 for socket 972
* 2015-07-24 08:28:57.564 (EFatal) **Terminated by user.**