How do I solve this problem, when generating my report with the library Html2pdf, on the first page it shows me this sign "?"

I have tried eliminating the tr where is the sql cosulta and the "?" in my report, but when I add the sql query it generates my report but it also generates this "?" in my report

vista_html.php

 <style >
    table { vertical-align: top; }
    tr    { vertical-align: top; }
    td    { vertical-align: top; }
    .midnight-blue{
        background:#2c3e50;
        padding: 4px 4px 4px;
        color:white;
        font-weight:bold;
        font-size:12px;
    }
    .silver{
        background:white;
        padding: 3px 4px 3px;
    }
    .clouds{
        background:#ecf0f1;
        padding: 3px 4px 3px;
    }
    .border-top{
        border-top: solid 1px #bdc3c7;

    }
    .border-left{
        border-left: solid 1px #bdc3c7;
    }
    .border-right{
        border-right: solid 1px #bdc3c7;
    }
    .border-bottom{
        border-bottom: solid 1px #bdc3c7;
    }
    table.page_footer {width: 100%; border: none; background-color: white; padding: 2mm;border-collapse:collapse; border: none;}
    }
    </style>

    <page backtop="15mm" backbottom="15mm" backleft="15mm" backright="15mm" style="font-size: 12pt; font-family: arial" >
        <page_header> 
             Page Header 
        </page_header> 
        <page_footer> 
             Page Footer 
        </page_footer> 

    <table cellspacing="0" style="width: 100%; text-align: left; font-size: 10pt;">
            <tr>
                <th style="width: 20%;text-align:center" class='midnight-blue'>CANT.</th>
                <th style="width: 60%" class='midnight-blue'>DESCRIPCION</th>
                <th style="width: 20%;text-align: right" class='midnight-blue'>PRECIO UNIT.</th>
            </tr>
                            <?php
                                $id= intval($_GET['id']);
                                require_once "./../config/Conexion.php";

                                $nums=1;
                                $sql=mysqli_query($conexion,"select * from cuota where id='".$id."'");
                                while ($row=mysqli_fetch_array($sql))
                                {
                                        $idd=$row[0];
                                        $nombre=$row[1];
                                        $cost=$row[2];
                                            if ($nums%2==0){
                                                $clase="clouds";
                                            } else {
                                                $clase="silver";
                                            }
                            ?>  
            <tr>
                <td class='<?php echo $clase;?>' style="width: 20%; text-align: center"><?php echo $idd;?></td>
                <td class='<?php echo $clase;?>' style="width: 60%; text-align: left"><?php echo $nombre;?></td>
                <td class='<?php echo $clase;?>' style="width: 20%; text-align: right"><?php echo $cost;?></td>
            </tr>
                            <?php   
                                    $nums++;              
                                    }
                            ?>


    </table>
    </page>

// my file where you call vista_html.php

<?php   

require __DIR__.'/../vendor/autoload.php';

use Spipu\Html2Pdf\Html2Pdf;
use Spipu\Html2Pdf\Exception\Html2PdfException;
use Spipu\Html2Pdf\Exception\ExceptionFormatter;

try {
    ob_start();
    include dirname(__FILE__).'/res/vista_html.php';
    $content = ob_get_clean();

    $html2pdf = new Html2Pdf('p', 'A4', 'es');
    $html2pdf->pdf->SetDisplayMode('fullpage');
    $html2pdf->writeHTML($content);
    $html2pdf->output('pdf_generate.pdf');
} catch (Html2PdfException $e) {
    $html2pdf->clean();

    $formatter = new ExceptionFormatter($e);
    echo $formatter->getHtmlMessage();
}

    ?>

// there an image