Active sub-menu item not displaying on Wordpress with Bootstrap - php

Question

Really struggling with this regarding sub-menus. I've made a custom theme for Wordpress using Bootstrap. I successfully managed to get to make my main nav menu dynamic with drop down sub menu links using wp_bootstrap_navwalker.
I've also made a nav-pills menu to display as a dynamic sub menu just below the main site nav menu and the page header. It shows all the child pages, of that particular parent.
My issue however, is that when you go on to a page with this menu, the active item on the menu does not display as active.
Here is my HTML/PHP:
<div class="nav-grey-band">
<?php
$args = array(
'menu' => 'primary',
'theme_location' => 'primary',
'submenu' => 'The Team',
'container_class' => 'centered-pills',
'menu_class' => 'nav nav-pills'
);
wp_nav_menu( $args );
?>
</div>
Here is what's in my functions.php:
// Register Custom Navigation Walker
require_once('wp_bootstrap_navwalker.php');
add_filter( 'wp_nav_menu_objects', 'submenu_limit', 10, 2 );
function submenu_limit( $items, $args ) {
if ( empty( $args->submenu ) ) {
return $items;
}
$ids = wp_filter_object_list( $items, array( 'title' => $args->submenu ), 'and', 'ID' );
$parent_id = array_pop( $ids );
$children = submenu_get_children_ids( $parent_id, $items );
foreach ( $items as $key => $item ) {
if ( ! in_array( $item->ID, $children ) ) {
unset( $items[$key] );
}
}
return $items;
}
function submenu_get_children_ids( $id, $items ) {
$ids = wp_filter_object_list( $items, array( 'menu_item_parent' => $id ), 'and', 'ID' );
foreach ( $ids as $id ) {
$ids = array_merge( $ids, submenu_get_children_ids( $id, $items ) );
}
return $ids;
}