Session renew not working

Good Morning together,

i have a problem in my written app.
I used the latest cakephp 2.x version.
My application runs in two tabs and in every tab runs a ajax / angularjs request to get json.
After few minutes the application kills the session and the user has to logon again!
here is my core.php

Configure::write(‘Session’, array(
‘defaults’ => ‘database’,
‘timeout’ => 30,
‘cookieTimeout’ => 1440,
‘checkAgent’ => false,
‘autoRegenerate’ => true,

Is this a known issue?
Is there a fix ?

regards thomas