Wordpress Gallery is not displaying

I have developed a custom wordpress theme from scratch. I'm having a issue in it. When I try to use native wordpress gallery shortcode in my post or page, It is display fine in the editor but its not displaying on the front end.

I even tried it by using:

echo do_shortcode('[gallery columns="5" link="none" ids="70,69,68,67"]');

But nothing has shown up...

Other post / page content is displaying fine but just gallery is not displaying. Its like its not even generating anything on the front-end.

If I switched the theme to any other theme it work but not in my theme, so its clear that its a theme problem. Do I have to add some kind of theme support for the gallery?

Any help would be appreciated :)

Update: 2 May, 2017

I'm using pre_get_posts hook which causing the problem. Can someone help me understand why?

Waited a lot but couldn't find an answer... I found the issue but doesn't know how to resolve it. But fortunately there is a way around it.

I have been using wordpress's pre_get_posts hook to set a tax_query which looks like this:

add_action( 'pre_get_posts', 'homeInjector' );

function homeInjector( $query ) {

        if ( $query->is_home() ) {

            $issues = get_terms( array(
                'taxonomy' => 'issues'
            ) );

            if ( isset( $_POST['issue'] ) ) {
                $term = $_POST['issue'];
            } else {
                $term = $issues[0]->slug;
            }


            $arg = array(
                array(
                    'taxonomy' => 'issues',
                    'terms'    => $term,
                    'field'    => 'slug'
                )
            );

            $query->set( 'tax_query', $arg );

        }

but if I use same code in index.php with new WP_Query object it works!

$issues = get_terms( array(
    'taxonomy' => 'issues'
) );

if ( isset( $_POST['issue'] ) ) {
    $term = $_POST['issue'];
} else {
    $term = $issues[0]->slug;
}

$qry = new WP_Query( array(
    'post_type' => 'post',
    'tax_query' => array(
        array(
            'taxonomy' => 'issues',
            'terms'    => $term,
            'field'    => 'slug'
        )
    )
) );

Don't know why but it works...

But still I'll wait for the appropriate answer because mine is just a way around to help me and others :)