bbPress.org

I am getting a HTTP ERROR 500 when I click on a Forum e.g.: https://ebps.org.uk/forums/forum/biology/
If I click on a post – it works, i.e: https://ebps.org.uk/forums/topic/sporangia-under-the-microscope/
If I click on “All Forums” from the dashboard, I get the 500 error
If I click on “NEW Forum” it works
The error_log says:
functions.php:1800
Stack trace:
#0 /var/sites/e/ebps.org.uk/public_html/wp-includes/class-wp-hook.php(298): bbp_pre_get_posts_normalize_forum_visibility(Object(WP_Query))
#1 /var/sites/e/ebps.org.uk/public_html/wp-includes/class-wp-hook.php(323): WP_Hook->apply_filters(NULL, Array)
#2 /var/sites/e/ebps.org.uk/public_html/wp-includes/plugin.php(515): WP_Hook->do_action(Array)
#3 /var/sites/e/ebps.org.uk/public_html/wp-includes/class-wp-query.php(1683): do_action_ref_array(‘pre_get_posts’, Array)
#4 /var/sites/e/ebps.org.uk/public_html/wp-includes/class-wp-query.php(3248): WP_Query->get_posts()
#5 /var/sites/e/ebps.org.uk/public_html/wp-includes/class-wp.php(617): WP_Query->query(Array)
#6 /var/sites/e/ebps.org.uk/public_html/wp-includes/class-wp.php(735): WP->query_posts()
#7 /var/sites/e/ebps.org.uk/public_html/wp-includes/functions.php(955): WP->main(”)
#8 /var/sites/e/ebp in /var/sites/e/ebps.org.uk/public_html/wp-content/plugins/bbpress/includes/forums/functions.php on line 1800

This is the code
1793 /** Default ***********************************************************/
1794
1795 // Get any existing post status
1796 $post_stati = $posts_query->get( ‘post_status’ );
1797
1798 // Default to public status
1799 if ( empty( $post_stati ) ) {
1800 $post_stati[] = bbp_get_public_status_id();

Any ideas?