WP_Query won’t return one of the custom post types when multiple post types requested

I’m registering multiple custom post types. One is ‘news’, the second is lets say ‘notification’. I’m registering both (and many others) with:

news:

$labels = .. // leaving this blank for SO, shouldn't be of importance

$args = array(
    'labels'             => $labels,
    'public'             => true,
    'publicly_queryable' => true,
    'show_ui'            => true,
    'show_in_menu'       => true,
    'query_var'          => true,
    'rewrite'            => array( 'slug' => 'news' ),
    'capability_type'    => 'post',
    'has_archive'        => true,
    'hierarchical'       => false,
    'menu_position'      => null,
    'supports'           => array( 'title', 'editor', 'author', 'thumbnail', 'excerpt', 'revisions' )
);

register_post_type( 'news', $args );

notification:

$labels = .. // leaving this blank for SO, shouldn't be of importance

$args = array(
    'labels'             => $labels,
    'public'             => true,
    'publicly_queryable' => true,
    'show_ui'            => true,
    'show_in_menu'       => true,
    'query_var'          => true,
    'rewrite'            => array( 'slug' => 'notification' ),
    'capability_type'    => 'post',
    'has_archive'        => true,
    'hierarchical'       => false,
    'menu_position'      => null,
    'supports'           => array( 'title', 'editor', 'author', 'thumbnail', 'excerpt', 'revisions' ),
    'can_export'         => true,
    'taxonomies'         => array('employee'),
);

register_post_type( 'notification', $args );

}

If I try to get for instance ‘news’ and ‘post’ post types (or ‘news’ and ‘event’ etc) like this

$args = array(
    'post_type' => array('news','post'),
);
$the_query = new WP_Query( $args );

it will do what it should: get all posts of the types given in post_type array param.

However, when I try to get any post type WITH ‘notification’ post type, it won’t return ‘notification’ post types. Examples I tried:

‘post_type’ => array(‘news’,’post’), // news AND posts get returned

‘post_type’ => array(‘news’,’notification’), // news get returned, but not notifications

‘post_type’ => array(‘post’,’notification’), // only posts get returned

When passing only ‘notification’ post type I get the posts returned as I should:

‘post_type’ => array(‘notification’), // I get all notifications

Why won’t I receive any post of type ‘notification’ if any other post type is present in post_type array? There must be something ridiculously obvious I’m missing here.

The only difference when registering news and notification is ‘can_export’ and ‘taxonomies’ but that is not it (tried commenting this out for notification)

Thank you

UPDATE

Ok so I think I have the culprit: Polylang Plugin. If deactivated, this works as it should. Any ideas?!