Navwalker深度= 2隐藏了父类别的下拉菜单

Question

为什么深度2隐藏我的父菜单而不显示任何子菜单，一旦我再次将其更改为1，它就显示父菜单但子菜单却没有显示。我也尝试更改我的js版本和引导程序，但仍然无法正常工作。我还检查了浏览器的控制台，但未发现错误。我正在使用bootstrap 3.3.7

    <nav class="nav navbar navbar-default navbar-right navbar-fixed-top" id="onscroll" role="navigation">

      <!-- Brand and toggle get grouped for better mobile display -->
      <div class="navbar-header">
        <button type="button" class="navbar-toggle" data-toggle="collapse" data-target="#bs-navbar-collapse-1">
          <span class="sr-only">Toggle navigation</span>
              <span class="icon-bar"></span>
              <span class="icon-bar"></span>
              <span class="icon-bar"></span>
        </button>
          <a class="navbar-brand" href="<?php echo home_url(); ?>"><img src="<?php echo get_stylesheet_directory_uri(); ?>/assets/img/logo.png" class="img-responsive" alt="xxxx"></a>
      </div>
            <?php
              // Menu Location
              wp_nav_menu( array(
                'menu'              => 'Primary',
                'theme_location'    => 'primary',
                'depth'             => 2,
                'container'         => 'div',
                'container_class'   => 'collapse navbar-collapse',
                'container_id'      => 'bs-example-navbar-collapse-1',
                'menu_class'        => 'nav navbar-nav navbar-right',
                'fallback_cb'       => 'wp_bootstrap_navwalker::fallback',
                'walker'            => new wp_bootstrap_navwalker())
               );
              ?>
      </div>
  </nav>

here's my functions.php 

    // Register Custom Navigation Walker
require('class-wp-bootstrap-navwalker.php');

register_nav_menus( array(
  'primary' => __( 'Primary', 'xxxxx-xxxxx' ),
) );
add_action( 'init', 'register_nav_menus' );