Hi there,
Access Denied indicates that you reached the resource, but for whatever reason, your access level/permissions were insufficient.
Make sure Authenticated Users were listed and have Read permission of SYSVOL folder. Also, make sure there is no Deny permission in the SYSVOL ACL list.
To schedule a Group Policy refresh to run on all computers in an OU by using the GPMC
https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-r2-and-2012/jj134201(v=ws.11)
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