If you open the portal, login via saml sso and do not open a udm-module, the session gets invalidated, because there is no /univention/get/session-info request. This does not happen, if you open a udm module. Because there is no request, the saml-session doesn't get refreshed and you get logged out after 5 minutes
*** This bug has been marked as a duplicate of bug 52334 ***