CodeIgniter不会加载特定的控制器

I am having a weird issue in which CodeIgniter (3.1) will not load a specific controller. I can load other controllers, but when I create a controller with the name sppb, using any case combination, and save the file as sppb.php it does not load.

<?php
    defined('BASEPATH') OR exit('No direct script access allowed');

   class Sppb extends CI_Controller {
      public function __construct()
      {
        parent::__construct();
      }

      public function index()
      {
      }
}

Above is the entire controller and it is saved to the server with the corresponding name of sppb.php.

I have also taken a different controller that I can load, copied it into a new file, changed the name to sppb, saved it to the server and it still will not load.

This is on a Linux server and I have checked the case in the naming of the file and the Controller.

Your Class file name needs to be 1st letter upper case... like

Sppb.php

The same applies to your class names

class Sppb extends CI_Controller {