session - PHP $_SESSION variable not working first time -

$_session['isloggedin'] doesn't seem working on first load.
happens on server, not on localhost.
session_start() @ top of each page.

initialized to: $_session['isloggedin'] = false;

when user logs in $_session['isloggedin'] = true;
when user logs out $_session['isloggedin'] = false;

on home.php:

if (!$_session['isloggedin']) {   die(header("location: login.php")); } 

on login.php:

if ($_session['isloggedin']) {   die(header("location: home.php")); } 

when login , sent home page $_session['isloggedin'] doesn't seem true redirects login.php. since true redirects home.php causing redirect loop.

when redirect loop error pops up, refresh , taken right page. page self refreshes , takes me correct page, still showing redirect error before.

why isn't $_session variable working on server? correct value doesn't seem register first time on every page, every site link.

edit:

everything works expected on localhost not on online server.
when login clicked , passes class login function called:

class users {      $_session['isloggedin'] = false;      function __construct() {         if (session_id() == "") {             session_start();         }          if (isset($_session['isloggedin']) && $_session['isloggedin'] == true) {             if (session_id() == '') {                 session_start();             }         }     }      function login($user,$password) {         if (session_id() == "") {             session_start();         }         $_session['isloggedin'] = false;          $mysqli = new mysqli(db_host, db_username, db_password, db_database);         if ($mysqli->connect_errno) {             return false;         }          $user = $mysqli->real_escape_string($user);         $password = $mysqli->real_escape_string($password);         $query = "select * users email=$user";          if (!$result = $mysqli->query($query)) {             return false;         }          $row = $result->fetch_assoc();         $db_pass = $row['password'];          if (crypt($password,$db_pass) != $db_pass) {             return false;         }          $_session['isloggedin'] = true;          if (session_id() == '') {             session_start();         }         return true;     }   } 

try changing code this

if (!isset($_session['isloggedin'])) {    header("location: login.php");  } else {    header("location: home.php"); }