Security log settings do not apply via GPO

Symptoms

When configuring maximum security event log size via Group Policy, you may notice that after the policy is applied, the log size on a specific computer is still not set to the value specified in the GPO (Group Policy Object).

Cause

A legacy registry setting overwrites the GPO.

Resolution

Open a regedit on the problematic server and check if the following key exists:

KEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\EventLog\Security\

The values inside this key, like MaxSize, are legacy and usually set by ADMX templates. Check in your current domain and local policies applied to the problematic computer if the following section is configured: Computer Configuration > Administrative Templates > Windows Components > Event Log Service > Security

The easiest way to find the right policy is using the gpresult tool.
To fix the issue, simply set the policy back to Not configured and execute gpupdate.