DOMPDF sometimes work,and sometimes not - php

Question

im using DOMPDF to make downloadable webpage.
but sometime it works, and Sometimes the page takes so long and finally displays "This site can not be reached, The connection was reset".
how to fix this?
its code error or its error on my webbrowser?
thanks :)
function __construct()
{
parent::__construct();
$this->load->model("Mproses");
}
public function download($db,$p,$id) {
// Load all views as normal
$data['hasil'] = $this->Mproses->selectWhere($db,$p,$id);
$this->load->view('hasil',$data);
// Get output html
$html = $this->output->get_output();
// Load library
$this->load->library('dompdf_gen');
$today = date('D-M-Y h:i:s');
// Convert to PDF
$this->dompdf->load_html($html);
$this->dompdf->render();
$this->dompdf->stream($today.".pdf",array('Attachment'=>1));
//or without preview in browser
//$this->dompdf->stream("welcome.pdf");
}
thats my controller for dompdf
HTML file im tryin to download :
<div class="row">
<div class="container">
<div class="col-md-8 col-md-offset-2">
<div class="panel panel-default">
<div class="panel-heading">
<h3 class="panel-title">Hasil Pengecekan! <p class="pull-right"><span class="fa fa-backward" aria-label="Kembali"></span> | <b>Kembali</b></p></h3>
</div>
<div class="panel-body">
<p style="color:black;">
<?php if(count($hasil)>0) { ?>
<?php foreach($hasil as $d) { ?>
<hr>
<br>
<center>
<h2 style="color:black;">Hasil Dari User : <?php echo $d->nama; ?></h2>
</center>
<br>
<hr>
<br>
<ul>
<li style="color:black;"><h5>Penyakit</h5><p style="font-size:20px;"><?php echo $d->penyakit;?></p></li>
<li style="color:black;"><h5>Pilihan</h5><p style="font-size:20px;">"<?php echo $d->pil;?>"</p></li>
<li style="color:black;"><h5>Nilai CF</h5><p style="font-size:20px;"><?php echo $d->nilaicf;?> || <?php echo $d->nilaicf*100;?>%</p></li>
</ul>
<?php } ?>
<?php } else { echo 'Maaf Data Yang Dicari Tidak Ada !'; } ?>
</p>
<br>
<hr>
<br>
<center><?php echo anchor(URL.'index.php/topdf/download/riwayat/id_riwayat/'.$d->id_riwayat,'Download',array('style' => 'color:black;font-size:14px;padding:14px;border:1px black solid;')); ?></center>
<br>
</div>
</div>
</div>
</div>
</div>