homepage redirects to login page when user session expires

If you looked at your plugins one by one and none of them causes the problem, look at your template files that display your home page – could be index.php, home.php, content.php, content-{slug/id}.php or page-templates/..., depending on your theme and settings.

Look for

if (!is_user_logged_in()) {
    auth_redirect();
}

or anything that seems to resemble this. It could be a shortcode or hook also, but its name will probably have something to do with user/login/auth.
If you found it, comment it out and reload, and see if it’s fixed.