Deployed Power Management options defined in the Group Policy Preferences (GPPs) are not applying on your Clients. Maybe other settings which are defined in the same Policy are working.
Check if you've configured the option apply once and do not reapply in the GPPs.
According to this article here is this behaviour a by design issue.
The Power Management options have to be applied two times. The first time the Power Plan gets created on your Client and at the second time the Plan is enabled. So if you've configured the above listed option the policy is only applied once and so the Power Management is not configured.
One option to get he Power Plan applied is to disable the "apply once and do not reapply" option. But in this case Power Plan changes from the Users are overwritten each time the policy is applied.
Another option is to create the following RegistryKey within the same Policy:
Value: cmd /c powercfg -s 381b4222-f694-41f0-9685-ff5bb260df2e
Make sure the Option "apply once and do not reapply" is also enabled for this Key. With this Workaround the PowerOptions are applied and enabled as soon as the User logs on to the client. If the policy is applied after the logon process, then the PowerOptions are enabled at the next logon