require_once raise HTTP ERROR 500 - php

Question

I'm working in a team on a e-shop website.
Recently, we've passed on Debian Jessie and from php5.4 to 5.6
Since then, we have multiple bug with require and require_once
Here's a file that raise an ERROR 500
<?php
require('/data/vhosts/mycompany.com/public_html/mp/../includes/functions/marketplace_tools.php');
//print_r(get_included_files());
require_once('/data/vhosts/mycompany.com/public_html/mp/../includes/functions/marketplace_tools.php');
echo 'pouet';
?>
The error.log say this :
PHP Fatal error: Cannot redeclare match_marketplace_products() in Cannot redeclare match_marketplace_products() on line 1
The filepath is good.
Marketplace_tools.php don't have require/include in
Marketplace_tools.php is just a bunch of function we use
If I run this file in command line, it works well
If I uncomment the print_r, it does not raise ERROR 500
This bug randomly appear and disapear

Answer 1

Cannot redeclare match_marketplace_products()
This error message tells you that there is a function name (match_marketplace_products) in the file you're including that already exists in the current PHP program.
You're using require_once(), but check that you haven't pulled in the same file elsewhere using require() (or include()).
Also check that the function name match_marketplace_products is only defined in this one file -- if it's defined in another file that is also included, then this will cause this error.