PHP Session Unsets Itself - php

Question

my session keeps getting unset, whenever I refresh a page, but when I made a control test it seemed to work fine.
Control(Held data):
<?php
session_start();
echo(var_dump($_SESSION));
$_SESSION['name'] = 'john doe';
?>
Top of index.php
<?php
session_start();
echo(var_dump($_SESSION));
include('utils/utils.php');
?>
Login page:
<?php
session_start();
include('utils.php');
if(isset($_POST['email']) && isset($_POST['password'])){
$email = filter($_POST['email']);
$password = getPwd(filter($_POST['password']));
if(!isset($_SESSION['email']) && !isset($_SESSION['password'])){
if(isAccount($email, $password)){
$key = genAuthKey();
$_SESSION['email'] = $email;
$_SESSION['auth_key'] = $key;
mysql_query("update `users` set `auth-key`= '$key' where `email`='$email'") or die(mysql_error());
print("ok");
}else {
print('error');
}
}else {
print('error');
logOut();
}
}else {
print('error');
}
?>
The code is getting fired, because it updated the auth-key in the table. I honestly have no idea what the issue is.
Also, the session is unset when I reload the index page.
I've got some more information. The pages can hold session data, and retain it, but once another page using session is loaded, it will unset all data.

Answer 1

Check if you use Unicode encoded PHP files with BOM.
PHP is not aware of the BOM. The BOM results in an output before your first <?php so PHP fails to set the related HTTP header for the session cookie.
From the docs:
To use cookie-based sessions, session_start() must be called before
outputing anything to the browser.