bbPress.org

well maybe there is a problem with recognizing the menu location , like exactly where the function is in loop-forums.php

first let me see a link to your website

then im going to recreate this bbpress menu from the steps i gave you and see if i made an error copying and pasting

by the time i finish this is what you could do

put <nav id="subnav" role="navigation">

<?php
if ( has_nav_menu( 'bbmenu' ) ) { /* if menu location 'bbmenu' exists then use custom menu */
      wp_nav_menu( array( 'theme_location' => 'bbmenu') ); 
}
?>

</nav>

below <?php do_action( 'bbp_template_before_forums_loop' ); ?>

and see if that fixes anything