Hi zbyszek
Thank you for bringing this issue to our attention.
To amend add the following to the end of your templates hornav.php (../templates/j51_renovate/php/layouts/hornav.php)...
<div id="hornavmobile" style="display:none;">
<?php echo $hornav_mobile ?>
</div>
And in your templates scripts.php (../templates/j51_renovate/php/scripts.php) replace the following (LINE 9)..
jQuery('#hornav').slicknav();
With..
jQuery('#hornavmobile').slicknav();
CiarĂ¡n