Description:
------------
This bug requires three files to reproduce, since it is an issue with spl_autoload_register(), specifically the prepend argument, and require_once().
Removing the prepend argument displays the expected result. 
This was created using a base install of PHP 7.1.10.

Test script:
---------------
---- file1.php ----
<?php
function load() { 
    spl_autoload_register('foo'); 
}
function foo($class) {
    echo __FUNCTION__ . "\n";
    require_once('./file2.php');
}
load();
new FooBar();

---- file2.php ----
<?php
function bar($class) {
    echo __FUNCTION__ . "\n";
    require_once('./file3.php');
}
spl_autoload_register('bar', true, true);

---- file3.php ----
<?php
class FooBar {
    public function __construct() { echo __CLASS__ . "\n"; }
}



Expected result:
----------------
foo
bar
FooBar

Actual result:
--------------
foo
foo
PHP Fatal error:  Uncaught Error: Class 'FooBar' not found in /home/user/phptest/file1.php:5
Stack trace:
#0 {main}
  thrown in /home/user/phptest/file1.php on line 5