Problem in Autoload PHP

Question

I’m starting to POO and SPL and recently faced the following problem: I have the following file that makes the whole bootstrapping of my application init.php, and in it, I do the autoload of all classes in the directory lib/:

set_include_path(get_include_path() 
              . PATH_SEPARATOR 
              . APP_ROOT_PATH 
              . DIRECTORY_SEPARATOR 
              . 'lib');
spl_autoload_extensions( ".php" );
spl_autoload_register();

However, it returns an error, always saying that some of the classes I later instated were not found:

/welcome.php - Uncaught Error: Class 'Hash' not found in /var/www/project/welcome.php:15

So, to debug, I made the following code:

spl_autoload_register(function($className){
    $className = str_replace('\\', DIRECTORY_SEPARATOR, $className);
    $file = $className . ".php";
    //echo 'Carregando arquivo ' . $file . PHP_EOL;
    require_once $file;
});

And in this way, it works perfectly, all my classes are imported! Someone has witnessed something similar?

Welcome.php

<?php

session_start();

define('APP_ROOT_PATH', dirname(__FILE__));

$configFiles = glob(APP_ROOT_PATH . DIRECTORY_SEPARATOR . 'config' . DIRECTORY_SEPARATOR . '*.php');

foreach($configFiles as $configFile){
    require_once $configFile;
}

set_include_path(get_include_path() . PATH_SEPARATOR . APP_ROOT_PATH . DIRECTORY_SEPARATOR . 'lib');
spl_autoload_extensions(".php");
//spl_autoload_register();
spl_autoload_register(function($className){
    $otherClassName = $className;
    $className = str_replace('\\', DIRECTORY_SEPARATOR, $className);
    $file = $className . ".php";
    //echo 'Carregando arquivo ' . $file . ' ' . $otherClassName . PHP_EOL;
    require_once $file;
});
//echo get_include_path();


require_once 'functions.php';


require_once 'vendor/autoload.php';

Folder structure: