Your Java code is not equivalent to your VB.NET code.

Java

Your use of PrintWriter does not guarantee UTF-8 encoding:

public void println(String x)

Prints a String and then terminates the line. This method behaves as though it invokes print(String) and then println().

public void print(String s)

Prints a string. If the argument is null then the string "null" is printed. Otherwise, the string's characters are converted into bytes according to the platform's default character encoding, and these bytes are written in exactly the manner of the write(int) method.

So, you are not guaranteed to be sending UTF-8. Instead, use OutputStreamWriter with a UTF-8 Charset assigned to it.

Also, you are sending 2 line terminators, one explicit in the string data and one implicit by println().

Try this:

try
{
    clientSocket = new Socket(ipaddress, portnumber);
    clientSocket.setKeepAlive(true);
    clientSocket.setSoTimeout(1000);

    outStreamSplunk = new BufferedWriter(new OutputStreamWriter(clientSocket.getOutputStream(), StandardCharsets.UTF_8));
    outStreamSplunk.write(post);
    if (!post.endsWith("\r\n"))
        outStreamSplunk.write("\r\n");
    outStreamSplunk.flush();

    System.out.println("SENT MESSAGE: " + post);

    clientSocket.close();
}
catch (Exception exc)
{
    // log exc.toString() as needed....
    return;
}

VB.NET

The code is forcing UTF-8, and only sends one line terminator. However, Environment.NewLine is platform-specific and not guaranteed to be a CRLF, so use vbCrLf instead.

Also, using IPAddress.Parse() to parse the result of AddressList(0).ToString() is redundant overhead since AddressList(0) returns an IPAddress to begin with, so just use it as-is.

Also, if Dns.GetHostEntry() or initialize() fails, you are not catching the exception to log it.

Try this:

'ip = "xxx.xxx.x.xxx"
'port = xxxx

Try
    _GLOIP = Dns.GetHostEntry(ip).AddressList(0)
    _port = port

    'initiate the client and get the stream to use
    myTcp = New TcpClient(New IPEndPoint(_GLOIP, _port))
    netStream = myTcp.GetStream() 

    Dim bufStream As BufferedStream = New BufferedStream(netStream)

    Dim sendBytes As Byte() = Encoding.UTF8.GetBytes(text)
    bufStream.Write(sendBytes, 0, sendBytes.Length)

    If Not text.EndsWith(vbCrLf) Then
        sendBytes = Encoding.UTF8.GetBytes(vbCrLf)
        bufStream.Write(sendBytes, 0, sendBytes.Length)
    End If

    bufStream.Flush()

Catch ex As Exception
    appLogs.constructLog(err & vbNewLine & ex.Message.ToString, True, True)
    Exit Sub
End Try

Alternatively, you could use the TcpClient constructor that accepts a string as input and not call Dns.GetHostEntry() at all:

'ip = "xxx.xxx.x.xxx"
'port = xxxx

_GLOIP = ip
_port = port

...

'initiate the client and get the stream to use
myTcp = New TcpClient(_GLOIP, _port)

Your flush is in the wrong place. It should be after the write, not before it, where it is completely pointless. Actually you should just close the writer instead of the socket: that wil flush the writer and close the socket. At present the data is never getting out of the writer into the socket.