Sporadic SFTP Upload Failure

A user is reporting sporadic failures with the log shown below. Any ideas on what could be causing this?

      InitializeSftp:
        DllDate: Jun 13 2016
        ChilkatVersion: 9.5.0.58
        UnlockPrefix: MLLTSFSSH
        Architecture: Little Endian; 32-bit
        Language: ActiveX
        VerboseLogging: 0
        sshTransportOpenChannel:
          channelType: session
          clientChannel: 0
          clientInitialWindowSize: 327680
          clientMaxPacketSize: 32768
          Sent open channel request
          sockRecv failed.
          sockRecvN_buf: Did not receive the exact number of bytes desired.
          numBytesToReceive: 16
          numBytesReceived: 0
          Failed to read 1st block_size bytes..
          Error reading channel response.
        --sshTransportOpenChannel
        SSH read timed out.
        Failed.
      --InitializeSftp
    --ChilkatLog