Error in Generating graph (using jpgraph) when graph code is placed after PDO SQL code

Question

In my PHP file I get rows from a mysql database table and then loop through them, store the values to an array and output it to the chart library (jpgraph). I get an error when checking this in the browser.

Here is the code:

<?php
require __DIR__.'/../../config/config.php';
// require_once ROOT_DIR.'/inc/functions.php';
require_once ROOT_DIR.'/inc/chart/jpgraph.php';
require_once ROOT_DIR.'/inc/chart/jpgraph_line.php';

$ticker = 'AAPL';

// Database
include_once(ROOT_DIR.'/inc/db_connect.php');
$dbname = "trade_stocks";

$table_name = 'agg_'.strtolower($ticker).'_min_1';



try {
    $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
    // set the PDO error mode to exception
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);  

    echo $conn->getAttribute(PDO::ATTR_CONNECTION_STATUS).PHP_EOL;

    if(!$conn) {
        echo 'Not connected';
    } else {
        echo 'DB Connected!'.PHP_EOL; 
    }

    $query = $conn->prepare("
        SELECT *
        FROM $table_name
        WHERE 
            start_date = '2022-07-19'
            AND start_time > '10:30:00'
            AND end_time < '15:50:00'
    ");
    $query->execute();
    $query->setFetchMode(PDO::FETCH_ASSOC);
    $stock_data = $query->fetchAll();

    // var_dump($stock_data);

    // Setup Chart
    $x_data = array();
    $y_data = array();
    foreach ($stock_data as $s_data) {
        $x_data[] = $s_data['start_time'];
        $y_data[] = floatval($s_data['close']);
    }

    $y_data = array_values($y_data);     

// complete and close connection
} // end try
    catch(PDOException $e) {
    echo "Connection failed: " . $e->getMessage().PHP_EOL;
}
$conn = null;

// Charting Code
// ------------------------------------------------------------------------

// Some data
$y_data = array(11,3,8,12,5,1,9,13,5,7);

// Create the graph. These two calls are always required
$graph = new Graph(3440,1440);
$graph->SetScale('textlin');

// Create the linear plot
$lineplot=new LinePlot($y_data);
$lineplot->SetColor('blue');

// Add the plot to the graph
$graph->Add($lineplot);

// Display the graph
$graph->Stroke();

When I move the charting code above the PDO mysql query, it works with a dummy data array.

// Chart a specific stock range
require __DIR__.'/../../config/config.php';
// require_once ROOT_DIR.'/inc/functions.php';
require_once ROOT_DIR.'/inc/chart/jpgraph.php';
require_once ROOT_DIR.'/inc/chart/jpgraph_line.php';

$ticker = 'AAPL';

// Database
include_once(ROOT_DIR.'/inc/db_connect.php');
$dbname = "trade_stocks";

$table_name = 'agg_'.strtolower($ticker).'_min_1';

// Charting Code
// ------------------------------------------------------------------------

// Some data
$y_data = array(11,3,8,12,5,1,9,13,5,7);

// Create the graph. These two calls are always required
$graph = new Graph(3440,1440);
$graph->SetScale('textlin');

// Create the linear plot
$lineplot=new LinePlot($y_data);
$lineplot->SetColor('blue');

// Add the plot to the graph
$graph->Add($lineplot);

// Display the graph
$graph->Stroke();


try {
    $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
    // set the PDO error mode to exception
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);  

    echo $conn->getAttribute(PDO::ATTR_CONNECTION_STATUS).PHP_EOL;

    if(!$conn) {
        echo 'Not connected';
    } else {
        echo 'DB Connected!'.PHP_EOL; 
    }

    $query = $conn->prepare("
        SELECT *
        FROM $table_name
        WHERE 
            start_date = '2022-07-19'
            AND start_time > '10:30:00'
            AND end_time < '15:50:00'
    ");
    $query->execute();
    $query->setFetchMode(PDO::FETCH_ASSOC);
    $stock_data = $query->fetchAll();

    // var_dump($stock_data);

    // Setup Chart
    $x_data = array();
    $y_data = array();
    foreach ($stock_data as $s_data) {
        $x_data[] = $s_data['start_time'];
        $y_data[] = floatval($s_data['close']);
    }

    $y_data = array_values($y_data);     

// complete and close connection
} // end try
    catch(PDOException $e) {
    echo "Connection failed: " . $e->getMessage().PHP_EOL;
}
$conn = null;

Testing without the charting, the code works. The PDO mysql query is somehow interfering with outputting the chart.