会话变量间歇性PHP

Question

I am trying to create a website and teach myself at the same time. I have implemented a database connection to allow users to register and sign in/out of the website but for some reason the session variables don't appear to be accessible from one specific page.

I have got the following php code on 2 pages that are in the same directory but the session vars are only accessible from one of the pages? Can anyone suggest what might be causing this and how this can be resolved?

<?php
// Initialize the session
session_start();
if(isset($_SESSION['username'])){echo "A";}
echo $_SESSION['username'];
?>

The initialisation of the username is done here:

if (password_verify($password, $row["password"])) { 
                session_start();
                $_SESSION['username'] = $username;
                $_SESSION['userType'] = $row["userType"];
                header("location: ../index.php");
            }

Answer 1

SOLVED:

In my navigation bar I was using a full URL instead of a relative link, this was causing a new session ID to be created and hence the session data was lost. Changing the nav bar to use relative paths meant the data wasn't lost