Nav walker issue? Nav disappears

[adambundy]

I am leveraging regular categories for a custom post type, so I've used the following to enable that post type for the category archives:

function tt_add_custom_types( $query ) {
  if( is_category() || is_tag() && empty( $query->query_vars['suppress_filters'] ) ) {
    $query->set( 'post_type', array(
     'post', 'newsitems'
        ));
      return $query;
    }
}
add_filter( 'pre_get_posts', 'tt_add_custom_types' );

...this works to enable those custom posts to show on the category term archive pages, but oddly, the nav is blank here. ??? The walker seems to somehow break on these pages - I end up with an empty .top-bar-section div - nothing in it.

Thanks!