Marker clustering on google map not working but all locations displayed?

Hi the issue im having is that marker clustering is not functioning but there are no errors in the console. however, the map ive created is displaying all the markers based off of data from an sql database which is converted from sql to xml via php, which is then requested from a js file which displays the markers. imm not sure if its the position of the markerclusterer in the js file or another issue. any advice would be great.

JS code

           function initMap() {
            var map = new google.maps.Map(document.getElementById('map'), {
                center: new google.maps.LatLng(51.8642112, -2.2380335),
                zoom: 11 
            });

            var infoWindow = new google.maps.InfoWindow();

            downloadUrl("./MapStolenDAO.php", function(data) {
                var xml = data.responseXML;
                var markers = xml.documentElement.getElementsByTagName('marker');
                Array.prototype.forEach.call(markers, function(markerElem) {
                var id = markerElem.getAttribute('id');
                var address = markerElem.getAttribute('address');
                var time = markerElem.getAttribute('time');
                var point = new google.maps.LatLng(
                    parseFloat(markerElem.getAttribute('lat')),
                    parseFloat(markerElem.getAttribute('lng')));

                var infowincontent = document.createElement('div');
                var strong = document.createElement('strong');
                strong.textContent = address
                infowincontent.appendChild(strong);
                infowincontent.appendChild(document.createElement('br'));

                var text = document.createElement('text');
                text.textContent = time
                infowincontent.appendChild(text);
                var marker = new google.maps.Marker({
                    position: point,
                    map: map
                });

                marker.addListener('click', function() {
                  infoWindow.setContent(infowincontent);
                  infoWindow.open(map, marker);
                });
                var markerCluster = new MarkerClusterer(map, [],
                    {imagePath: './mapImages'});
            });
        });
    }

    function downloadUrl(url, callback) {
        var request = window.ActiveXObject ?
            new ActiveXObject('Microsoft.XMLHTTP') :
            new XMLHttpRequest();

        request.onreadystatechange = function() {

**SQL to XML via PHP code **

<?php
$username="username is here but removed for privacy";
$password="password is here but removed for privacy";
$database="DBFlogger";

function parseToXML($htmlStr)
{
$xmlStr=str_replace('<','&lt;',$htmlStr);
$xmlStr=str_replace('>','&gt;',$xmlStr);
$xmlStr=str_replace('"','&quot;',$xmlStr);
$xmlStr=str_replace("'",'&#39;',$xmlStr);
$xmlStr=str_replace("&",'&amp;',$xmlStr);
return $xmlStr;
}

// Opens a connection to a MySQL server
$connection = mysqli_connect('localhost', $username, $password);
if (!$connection) {
    error_log("Failed to connect to MySQL: " . mysqli_error($connection));
    die('Internal server error');
}

// Set the active MySQL database
$db_selected = mysqli_select_db($connection, $database);
if (!$db_selected) {
    error_log("Database selection failed: " . mysqli_error($connection));
    die('Internal server error');
}

// Select all the rows in the markers table
$query = "SELECT * FROM tblBikeStolen WHERE 1";
$result = mysqli_query($connection, $query);
if (!$result) {
    error_log("Database query failed:" . mysqli_error($connection));
    die('Internal server error');
}

header("Content-type: text/xml");

// Start XML file, echo parent node
echo "<?xml version='1.0' ?>";
echo '<markers>';
$ind=0;
// Iterate through the rows, printing XML nodes for each
while ($row = @mysqli_fetch_assoc($result)){
  // Add to XML document node
  echo '<marker ';
  echo 'id="' . $row['BikeID'] . '" ';
  echo 'address="' . parseToXML($row['Address']) . '" ';
  echo 'lat="' . $row['Lat'] . '" ';
  echo 'lng="' . $row['Lng'] . '" ';
  echo 'time="' . $row['stolenTimestamp'] . '" ';
  echo '/>';
  $ind = $ind + 1;
}

// End XML file
echo '</markers>';

?>

HTML file

<!DOCTYPE html>
<html>
<head>
<title></title>
<link rel="stylesheet" type="text/css" href="../../styles.css">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
<script src="https://kit.fontawesome.com/57cdec9607.js" crossorigin="anonymous"></script>

</head>
<body>
<header>
    <a href="" style="float:left">BIKEIT!</a>
    <a href="../Public/Contacts.html">CONTACT</a>
    <a href="../Public/AboutUs.html">ABOUT</a>
    <a href="../Public/FAQ.html">FAQ</a>
    <a href="../Police/Police_Home.html">HOME</a>
</header>
<div id="master"></div>
<h1 style="color: white; margin: 10px; text-align: center">Victim Location Frequency Map</h1>
<div id="content">
    <div id="map" style="width:60%;height:700px;"></div>

        <script src="MapStolen.js"></script>

        <script src="https://unpkg.com/@google/markerclustererplus@4.0.1/dist/markerclustererplus.min.js"></script>

        <script async defer
        src="https://maps.googleapis.com/maps/api/js?key=AIzaSyAFkcR79QqNX1TuaLjSCmfgdSujOeYt1FU&callback=initMap">
        </script>

    </div>
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