Thank you for letting us know. I let developers known about the issue, and it will be fixed in the near feature.

File: wpforo/wpf-includes/integration/buddypress.php:684

In function wpforo_bp_buddypress_mark_notifications we have:

if ( isset($wp_error) && !is_wp_error($wp_error) ) {
 $success = bp_notifications_mark_notifications_by_item_id( $user_id, $reply_id, 'community', 'wpforo_new_reply' );
 do_action( 'wpforo_bp_notifications_handler', $success, $user_id, $reply_id, $action );
}

Since $wp_error is only defined in the event that there either !$result or !current_user_can( 'edit_user', $user_id ), the contents of the above if statement are never run. (If there isn't an error, then $wp_error is not set)

As a consequence, notifications are not cleared on action wpforo_mark_read.

Thankyou.