In the provided PHP code snippet, what could be causing the user to be redirected to the login page even after successfully logging in on a different PC?

The issue could be due to the use of session variables that are not being properly stored or checked across different devices. To solve this issue, make sure that the session_start() function is called at the beginning of every page where session variables are used. Additionally, ensure that the session variables are being properly set and checked for on each page to maintain the user's login status.

// Fix for maintaining user login status across different devices
session_start();

// Check if the user is logged in
if(isset($_SESSION['user_id'])) {
    // User is logged in, continue with the current page
} else {
    // User is not logged in, redirect to the login page
    header("Location: login.php");
    exit();
}