Windows Built upgrade from 1511 to 21h2 issue

Hi Team,

Greetings !!

We are facing a issue which is a different kind of issue in our environment. In our environment there are various Windows builds from 1511,1609,1709 and 1909. We are trying to upgrade the Windows built with the help of fixlet which is present in the BigFix console.

The issue which we are facing is that when we are deploying the fixlet on windows 1511 version the task get completed but after restart the OS version does not gets upgraded but when we deploy the same fixlet on Windows 1909 system the OS gets upgraded to 20h2.

Is there anything which i am missing in the deployment, any help to resolve this issue will be helpful.

Thanks in advance,
Regards,
KK