Here is the updated log:
2019-03-22 08:53:35.308 Opening log file.
2019-03-22 08:53:35.311 INFO FileLogWriter(2)[6] Info: Assembly: Rebex.Common 2017 R6.3 for .NET 2.0-3.5
2019-03-22 08:53:35.312 INFO FileLogWriter(2)[6] Info: Platform: Windows 6.2.9200 32-bit; CLR: 2.0.50727.9035
2019-03-22 08:53:35.312 DEBUG FileLogWriter(2)[6] Info: Culture: en; Windows-1252
2019-03-22 08:53:35.326 INFO SftpKeepAlive(1)[6] Info: Connecting to oracle12c:22 using Sftp.
2019-03-22 08:53:35.328 INFO SftpKeepAlive(1)[6] Info: Assembly: Rebex.Sftp 2017 R6.3 for .NET 2.0-3.5
2019-03-22 08:53:35.329 INFO SftpKeepAlive(1)[6] Info: Platform: Windows 6.2.9200 32-bit; CLR: 2.0.50727.9035
2019-03-22 08:53:35.330 DEBUG SftpKeepAlive(1)[6] Info: Culture: en; Windows-1252
2019-03-22 08:53:35.360 DEBUG ProxySocket(1)[6] Proxy: Resolving 'oracle12c'.
2019-03-22 08:53:35.413 DEBUG ProxySocket(1)[6] Proxy: Connecting to none proxy at 10.10.10.60:22.
2019-03-22 08:53:35.434 DEBUG SftpKeepAlive(1)[6] SSH: Server is 'SSH-2.0-WeOnlyDo 2.4.3'.
2019-03-22 08:53:35.450 INFO SftpKeepAlive(1)[6] SSH: Negotiation started.
2019-03-22 08:53:35.543 DEBUG SftpKeepAlive(1)[6] SSH: Negotiating key.
2019-03-22 08:53:35.581 DEBUG SftpKeepAlive(1)[6] SSH: Using 2048-bit Diffie-Hellman prime (minimum allowed size is 1024 bits).
2019-03-22 08:53:35.814 DEBUG SftpKeepAlive(1)[6] SSH: Validating signature.
2019-03-22 08:53:35.879 INFO SftpKeepAlive(1)[6] SSH: Negotiation finished.
2019-03-22 08:53:35.880 INFO SftpKeepAlive(1)[6] Info: Server: SSH-2.0-WeOnlyDo 2.4.3
2019-03-22 08:53:35.882 INFO SftpKeepAlive(1)[6] Info: Fingerprint (MD5): 90:05:6e:67:ea:01:b4:e3:aa:89:83:ca:a9:dd:63:3c
2019-03-22 08:53:35.887 INFO SftpKeepAlive(1)[6] Info: Fingerprint (SHA-256): x6kGY2PXDCvRhrOv30P/+1Ri6C4XDKu10YmcrmwESnA
2019-03-22 08:53:35.889 INFO SftpKeepAlive(1)[6] Info: Cipher info: SSH 2.0, diffie-hellman-group14-sha1, ssh-dss, aes256-ctr/aes256-ctr, hmac-sha2-256/hmac-sha2-256
2019-03-22 08:53:35.907 DEBUG SftpKeepAlive(1)[6] SSH: Allowed authentication methods for 'user1': password, gssapi-with-mic, publickey.
2019-03-22 08:53:35.909 DEBUG SftpKeepAlive(1)[6] SSH: Trying password authentication for 'user1'.
2019-03-22 08:53:35.913 DEBUG SftpKeepAlive(1)[6] SSH: Authentication successful.
2019-03-22 08:53:35.923 DEBUG SftpKeepAlive(1)[6] SSH: Requesting subsystem 'sftp'.
2019-03-22 08:53:35.933 INFO SftpKeepAlive(1)[6] Command: SSH_FXP_INIT (4)
2019-03-22 08:53:35.975 INFO SftpKeepAlive(1)[6] Response: SSH_FXP_VERSION (3, 0 extensions)
2019-03-22 08:53:35.977 INFO SftpKeepAlive(1)[6] Info: Using SFTP v3 on a Windows-like platform.
2019-03-22 08:53:35.983 INFO SftpKeepAlive(1)[6] Command: SSH_FXP_STAT (1, '/BigFile.txt')
2019-03-22 08:53:35.987 INFO SftpKeepAlive(1)[6] Response: SSH_FXP_ATTRS (1)
2019-03-22 08:53:35.990 INFO SftpKeepAlive(1)[6] Command: SSH_FXP_STAT (2, '/BigFile.txt')
2019-03-22 08:53:35.991 INFO SftpKeepAlive(1)[6] Response: SSH_FXP_ATTRS (2)
2019-03-22 08:53:35.999 INFO SftpKeepAlive(3)[6] Info: Connecting to oracle12c:22 using Sftp.
2019-03-22 08:53:36.001 INFO SftpKeepAlive(3)[6] Info: Assembly: Rebex.Sftp 2017 R6.3 for .NET 2.0-3.5
2019-03-22 08:53:36.002 INFO SftpKeepAlive(3)[6] Info: Platform: Windows 6.2.9200 32-bit; CLR: 2.0.50727.9035
2019-03-22 08:53:36.003 DEBUG SftpKeepAlive(3)[6] Info: Culture: en; Windows-1252
2019-03-22 08:53:36.004 DEBUG ProxySocket(2)[6] Proxy: Resolving 'oracle12c'.
2019-03-22 08:53:36.007 DEBUG ProxySocket(2)[6] Proxy: Connecting to none proxy at 10.10.10.60:22.
2019-03-22 08:53:36.012 DEBUG SftpKeepAlive(3)[6] SSH: Server is 'SSH-2.0-WeOnlyDo 2.4.3'.
2019-03-22 08:53:36.014 INFO SftpKeepAlive(3)[6] SSH: Negotiation started.
2019-03-22 08:53:36.015 DEBUG SftpKeepAlive(3)[6] SSH: Negotiating key.
2019-03-22 08:53:36.047 DEBUG SftpKeepAlive(3)[6] SSH: Using 2048-bit Diffie-Hellman prime (minimum allowed size is 1024 bits).
2019-03-22 08:53:36.284 DEBUG SftpKeepAlive(3)[6] SSH: Validating signature.
2019-03-22 08:53:36.287 INFO SftpKeepAlive(3)[6] SSH: Negotiation finished.
2019-03-22 08:53:36.288 INFO SftpKeepAlive(3)[6] Info: Server: SSH-2.0-WeOnlyDo 2.4.3
2019-03-22 08:53:36.289 INFO SftpKeepAlive(3)[6] Info: Fingerprint (MD5): 90:05:6e:67:ea:01:b4:e3:aa:89:83:ca:a9:dd:63:3c
2019-03-22 08:53:36.290 INFO SftpKeepAlive(3)[6] Info: Fingerprint (SHA-256): x6kGY2PXDCvRhrOv30P/+1Ri6C4XDKu10YmcrmwESnA
2019-03-22 08:53:36.291 INFO SftpKeepAlive(3)[6] Info: Cipher info: SSH 2.0, diffie-hellman-group14-sha1, ssh-dss, aes256-ctr/aes256-ctr, hmac-sha2-256/hmac-sha2-256
2019-03-22 08:53:36.293 DEBUG SftpKeepAlive(3)[6] SSH: Allowed authentication methods for 'user1': password, gssapi-with-mic, publickey.
2019-03-22 08:53:36.294 DEBUG SftpKeepAlive(3)[6] SSH: Trying password authentication for 'user1'.
2019-03-22 08:53:36.297 DEBUG SftpKeepAlive(3)[6] SSH: Authentication successful.
2019-03-22 08:53:36.300 DEBUG SftpKeepAlive(3)[6] SSH: Requesting subsystem 'sftp'.
2019-03-22 08:53:36.304 INFO SftpKeepAlive(3)[6] Command: SSH_FXP_INIT (4)
2019-03-22 08:53:36.345 INFO SftpKeepAlive(3)[6] Response: SSH_FXP_VERSION (3, 0 extensions)
2019-03-22 08:53:36.348 INFO SftpKeepAlive(3)[6] Info: Using SFTP v3 on a Windows-like platform.
2019-03-22 08:53:36.355 INFO SftpKeepAlive(3)[6] Command: SSH_FXP_OPEN (1, '/BigFile.txt', 1)
2019-03-22 08:53:36.357 INFO SftpKeepAlive(3)[6] Response: SSH_FXP_HANDLE (1, 0x776F645366747046696C6548616E646C6530)
2019-03-22 08:53:36.370 ERROR SftpKeepAlive(3)[6] SSH: Rebex.Net.SshException: The SSH connection failed.
at Rebex.Net.SshSession.PF(PE I, Boolean J)
at Rebex.Net.SshChannel.DJ(PE I)
at Rebex.Net.SshChannel.Send(Byte[] buffer, Int32 offset, Int32 count)
2019-03-22 08:53:36.373 ERROR SftpKeepAlive(3)[6] SSH: Rebex.Net.SshException: The channel has been closed.
at Rebex.Net.SshChannel.Send(Byte[] buffer, Int32 offset, Int32 count)