PHP session cookies in a subdomain using IE11/Safari

I’m losing the session between redirects in both Internet Explorer 11 and Safari (works fine on Chrome, Opera and Firefox).

When I try to login using www.subdomain.domain.com the error occurs on IE/Safari, but even on them it works fine if I use the IP (xxx.xxx.xxx.xxx/folder).

I’m trying to setup the session like:

session_name("somename");
session_set_cookie_params(3600, '/folder/');
session_start();

I have already tried:

session_set_cookie_params(3600, '/folder/', '.domain.com);
session_set_cookie_params(3600, '/folder/', '.subdomain.domain.com);
session_set_cookie_params(3600, '/folder/', 'domain.com);  <-- without the preceding dot
session_set_cookie_params(3600, '/folder/', 'subdomain.domain.com);
ini_set("session.cookie_domain", ".domain.com"); <-- before set_cookie_params

But none of them seems to work.