Carousel not working with post_gallery filter

In a child theme I’m working on, I hooked the post_gallery filter to change how galleries appeared by default. By result, Jetpack Carousel won’t even start. It depends on the function, because when I dismiss it Carousel works again. In this website I left the function so you can see: https://www.andywar.net/runningcomics/
Below is function:

<?php
function andywar_gallery_shortcode($empty , $attr) {

// We're trusting author input, so let's at least make sure it looks like a valid orderby statement
if ( isset( $attr['orderby'] ) ) {
$attr['orderby'] = sanitize_sql_orderby( $attr['orderby'] );
if ( !$attr['orderby'] )
unset( $attr['orderby'] );
}

extract(shortcode_atts(array(
'order'      => 'ASC',
'orderby'    => 'menu_order ID',
'id'         => $post ? $post->ID : 0,
'itemtag'    => 'dl',
'icontag'    => 'dt',
'captiontag' => 'dd',
'columns'    => 2,
'size'       => 'medium',
'include'    => '',
'exclude'    => '',
'link'       => ''
), $attr, 'gallery'));

$id = intval($id);
if ( 'RAND' == $order )
$orderby = 'none';

if ( !empty($include) ) {
$_attachments = get_posts( array('include' => $include, 'post_status' => 'inherit', 'post_type' => 'attachment', 'post_mime_type' => 'image', 'order' => $order, 'orderby' => $orderby) );

$attachments = array();
foreach ( $_attachments as $key => $val ) {
$attachments[$val->ID] = $_attachments[$key];
}
} elseif ( !empty($exclude) ) {
$attachments = get_children( array('post_parent' => $id, 'exclude' => $exclude, 'post_status' => 'inherit', 'post_type' => 'attachment', 'post_mime_type' => 'image', 'order' => $order, 'orderby' => $orderby) );
} else {
$attachments = get_children( array('post_parent' => $id, 'post_status' => 'inherit', 'post_type' => 'attachment', 'post_mime_type' => 'image', 'order' => $order, 'orderby' => $orderby) );
}

if ( empty($attachments) )
return '';

if ( is_feed() ) {
$output = "\n";
foreach ( $attachments as $att_id => $attachment )
$output .= wp_get_attachment_link($att_id, $size, true) . "\n";
return $output;
}

$itemtag = tag_escape($itemtag);
$captiontag = tag_escape($captiontag);
$icontag = tag_escape($icontag);
$valid_tags = wp_kses_allowed_html( 'post' );
if ( ! isset( $valid_tags[ $itemtag ] ) )
$itemtag = 'dl';
if ( ! isset( $valid_tags[ $captiontag ] ) )
$captiontag = 'dd';
if ( ! isset( $valid_tags[ $icontag ] ) )
$icontag = 'dt';

$columns = intval($columns);
$itemwidth = $columns > 0 ? floor(100/$columns) : 100;
$float = is_rtl() ? 'right' : 'left';

$selector = "gallery-{$instance}";

$gallery_style = $gallery_div = '';
if ( apply_filters( 'use_default_gallery_style', true ) )
$gallery_style = "
<style type='text/css'>
#{$selector} {
margin: auto;
}
#{$selector} .gallery-item {
float: {$float};
margin-top: 10px;
text-align: center;
width: {$itemwidth}%;
}
#{$selector} img {
border: 2px solid #cfcfcf;
}
#{$selector} .gallery-caption {
margin-left: 0;
}
/* see gallery_shortcode() in wp-includes/media.php */
</style>";
$size_class = sanitize_html_class( $size );
$gallery_div = "<div id='$selector' class='gallery galleryid-{$id} gallery-columns-{$columns} gallery-size-{$size_class}'>";
$output = apply_filters( 'gallery_style', $gallery_style . "\n\t\t" . $gallery_div );

$i = 0;
foreach ( $attachments as $id => $attachment ) {
if ( ! empty( $link ) && 'file' === $link )
$image_output = wp_get_attachment_link( $id, $size, false, false );
elseif ( ! empty( $link ) && 'none' === $link )
$image_output = wp_get_attachment_image( $id, $size, false );
else
$image_output = wp_get_attachment_link( $id, $size, true, false );

$image_meta  = wp_get_attachment_metadata( $id );

$orientation = '';
if ( isset( $image_meta['height'], $image_meta['width'] ) )
$orientation = ( $image_meta['height'] > $image_meta['width'] ) ? 'portrait' : 'landscape';

$output .= "<{$itemtag} class='gallery-item'>";
$output .= "
<{$icontag} class='gallery-icon {$orientation}'>
$image_output
</{$icontag}>";
if ( $captiontag && trim($attachment->post_excerpt) ) {
$output .= "
<{$captiontag} class='wp-caption-text gallery-caption'>
" . wptexturize($attachment->post_excerpt) . "
</{$captiontag}>";
}
$output .= "</{$itemtag}>";
if ( $columns > 0 && ++$i % $columns == 0 )
$output .= '<br style="clear: both" />';
}

$output .= "
<br style='clear: both;' />
</div>\n";

return $output;
}

add_filter('post_gallery' , 'andywar_gallery_shortcode' , 10 , 2);
?>