Foreach loop not always displaying - php

Question

I'm retrieving data out of a database using PHP's PDO extension. I never had a problem with this and it always shows up in all browsers. BUT when I tested the website on a friends laptop, the foreach loop works but the content is not displayed. The content is present in the source code.
this is how I set up the code that should be displayed:
<?php
foreach($advertentiesManager->recenteAdvertenties() as $advertentie) {
$verkoperData = $usersManager->userData($advertentie->verkoper);
?>
<div class="col-md-4" style="margin:10px 0;">
<div class="advertentie">
<div class="overlay"></div>
<div class="img" style="background:url('images/categorie/<?php echo $advertentie->categorie; ?>.jpg') no-repeat center center;background-size:cover;"></div>
<div class="picture" style="background:url('<?php echo str_replace("../", "", $verkoperData->foto); ?>') no-repeat center center;background-size:cover;"></div>
<div class="prijs"><p class="h2">€ <?php echo $advertentie->verkoopprijs; ?></p></div>
<div style="padding: 10px;padding-left:80px;margin-top:-40px;">
<a href="<?php echo $advertentie->type.'/'.strtolower(str_replace(" ", "-", $advertentie->titel)).'-'.$advertentie->id; ?>">
<?php echo $advertentie->titel; ?>
</a>
<br>
<p style="color:#777;font-size:.9em;">
<?php
$beschrijving = strip_tags($advertentie->omschrijving);
$max_length = 100;
if (strlen($beschrijving) > $max_length) {
$offset = ($max_length - 3) - strlen($beschrijving);
$beschrijving = substr($beschrijving, 0, strrpos($beschrijving, ' ', $offset)) . '... Meer';
} else {
$beschrijving = $advertentie->omschrijving;
}
echo $beschrijving;
?>
</p>
</div>
</div>
</div>
<?php
}
?>
You can view a live example at http://www.coupontrade.nl/ the content should be displayed under "Recente advertenties" and above the twitter part.