I'm having a problem with my theme's compatibility with bootstrap.

So the checkboxes on my website appear double ().

So I enqueued the latest Bootstrap CDN (CSS and Scripts) on my child theme and now the buttons are fixed but the drop down ul doesn't work as intended. Instead of opening the dropdown, it goes to the link.

Here's the dropdown ul code:

<a class="user-link" href="<?php echo $user_link; ?>">
 <span class="user-name"><?php echo $current_user->display_name; ?></span><i class="bb-icon-angle-down"></i>
    <?php echo get_avatar( get_current_user_id(), 35); ?>
</a>

<ul class="sub-menu">
 <li>
  <a class="user-link" href="<?php echo $user_link; ?>">
    <?php echo get_avatar( get_current_user_id(), 35); ?>
        <span>
         <span class="user-name"><?php echo $current_user->display_name; ?></span>
            <?php if( function_exists( 'bp_is_active' ) ) : ?>
                                    <span class="user-mention"><?php echo '@' . bp_activity_get_user_mentionname( $current_user->ID ); ?></span>
                                <?php else : ?>
              <span class="user-mention"><?php echo '@' . $current_user->user_login; ?></span>
            <?php endif; ?>
              </span>
  </a>
 </li>
 <?php do_action( THEME_HOOK_PREFIX . 'header_user_menu_items' ); ?>
</ul>