Why does Sftp.GetFile work but Sftp.GetDownloadStream does not?

Here's the log file when using GetDownloadStream:

INFO FileLogWriter(2)[6] Info: Assembly: Rebex.Common 2017 R6.3 for .NET 2.0-3.5
INFO FileLogWriter(2)[6] Info: Platform: Windows 6.2.9200 32-bit; CLR: 2.0.50727.9035
INFO SftpKeepAlive(1)[6] Info: Connecting to oracle12c:22 using Sftp.
INFO SftpKeepAlive(1)[6] Info: Assembly: Rebex.Sftp 2017 R6.3 for .NET 2.0-3.5
INFO SftpKeepAlive(1)[6] Info: Platform: Windows 6.2.9200 32-bit; CLR: 2.0.50727.9035
INFO SftpKeepAlive(1)[6] SSH: Negotiation started.
INFO SftpKeepAlive(1)[6] SSH: Negotiation finished.
INFO SftpKeepAlive(1)[6] Info: Server: SSH-2.0-WeOnlyDo 2.4.3
INFO SftpKeepAlive(1)[6] Info: Fingerprint (MD5): 90:05:6e:67:ea:01:b4:e3:aa:89:83:ca:a9:dd:63:3c
INFO SftpKeepAlive(1)[6] Info: Fingerprint (SHA-256): x6kGY2PXDCvRhrOv30P/+1Ri6C4XDKu10YmcrmwESnA
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
INFO SftpKeepAlive(1)[6] Command: SSH_FXP_INIT (4)
INFO SftpKeepAlive(1)[6] Response: SSH_FXP_VERSION (3, 0 extensions)
INFO SftpKeepAlive(1)[6] Info: Using SFTP v3 on a Windows-like platform.
INFO SftpKeepAlive(1)[6] Command: SSH_FXP_STAT (1, '/BigFile.txt')
INFO SftpKeepAlive(1)[6] Response: SSH_FXP_ATTRS (1)
INFO SftpKeepAlive(1)[6] Command: SSH_FXP_STAT (2, '/BigFile.txt')
INFO SftpKeepAlive(1)[6] Response: SSH_FXP_ATTRS (2)
INFO SftpKeepAlive(3)[6] Info: Connecting to oracle12c:22 using Sftp.
INFO SftpKeepAlive(3)[6] Info: Assembly: Rebex.Sftp 2017 R6.3 for .NET 2.0-3.5
INFO SftpKeepAlive(3)[6] Info: Platform: Windows 6.2.9200 32-bit; CLR: 2.0.50727.9035
INFO SftpKeepAlive(3)[6] SSH: Negotiation started.
INFO SftpKeepAlive(3)[6] SSH: Negotiation finished.
INFO SftpKeepAlive(3)[6] Info: Server: SSH-2.0-WeOnlyDo 2.4.3
INFO SftpKeepAlive(3)[6] Info: Fingerprint (MD5): 90:05:6e:67:ea:01:b4:e3:aa:89:83:ca:a9:dd:63:3c
INFO SftpKeepAlive(3)[6] Info: Fingerprint (SHA-256): x6kGY2PXDCvRhrOv30P/+1Ri6C4XDKu10YmcrmwESnA
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
INFO SftpKeepAlive(3)[6] Command: SSH_FXP_INIT (4)
INFO SftpKeepAlive(3)[6] Response: SSH_FXP_VERSION (3, 0 extensions)
INFO SftpKeepAlive(3)[6] Info: Using SFTP v3 on a Windows-like platform.
INFO SftpKeepAlive(3)[6] Command: SSH_FXP_OPEN (1, '/BigFile.txt', 1)
INFO SftpKeepAlive(3)[6] Response: SSH_FXP_HANDLE (1, 0x776F645366747046696C6548616E646C6530)
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)
ERROR SftpKeepAlive(3)[6] SSH: Rebex.Net.SshException: The channel has been closed.
   at Rebex.Net.SshChannel.Send(Byte[] buffer, Int32 offset, Int32 count)