Internet Explorer Group Policy Preferences problem
I accidently set the Security Zones to the default values in Group Policy preferences when I was changing another setting. Didn't noticed the problem on test bed.
This morning this manifested as 'High' for the Internet Zone but after changing it to a lower value (all the users were seeing a lot of security warnings and pages were not loading correctly) now it will not apply anything but a 'Custom' security level even though the policy is applying correctly.
Tried removing the GPO completely, recreating with the correct settings - nothing seems to actually apply.