Method always returns the same value (cache?)

Can't reproduce.

Code:

$ php public/index.php
almjv976uc
$ php public/index.php
o51xgm4l6e
$ php public/index.php
igcjb9h8kt
$ php -v
PHP 8.0.15 (cli) (built: Jan 20 2022 04:25:44) ( NTS )
Copyright (c) The PHP Group
Zend Engine v4.0.15, Copyright (c) Zend Technologies
    with Xdebug v3.1.1, Copyright (c) 2002-2021, by Derick Rethans
    with Zend OPcache v8.0.15, Copyright (c), by Zend Technologies

PHP Code:

<?php

namespace App\Controllers;

class Home extends BaseController
{
    public function index()
    {
        echo RS_RANDOM_STRING(10) . PHP_EOL;
    }
}

function RS_RANDOM_STRING(int $length, bool $onlyLetters = false, bool $onlyNumbers = false): string
{
    $chars = '';
    if (!$onlyNumbers || $onlyLetters) $chars .= 'abcdefghijklmnopqrstuvwxyz';
    if (!$onlyLetters || $onlyNumbers) $chars .= '0123456789';

    $numChars = strlen($chars);
    $loop = ceil($length / $numChars);

    return substr(str_shuffle(str_repeat($chars, $loop)), 0, $length);
} 


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