For instance, we’re now seeing reports that after Windows 10 version 1809 is installed on PCs the OS is no longer activated, in which case a watermark shows up on the desktop.
There are two different problems in such a case. First of all, there are users who no longer have the product key for their system and extracting it from Windows 10 isn’t possible because the system isn’t activated.
The only workaround is to go back to the previous Windows 10 version using the rolling back feature in the OS and then extract the product key, only to reinstall the October 2018 Update and then activate it manually. However, keep in mind that the October update isn’t available right now, and you may have to wait a while until the rollout resumes.

Product key issues

Also, it turns out that on some devices, the product key isn’t working anymore and Windows 10 cannot be reactivated after installing the October 2018 Update.
However, we’re seeing just isolated reports in this regard, as it’s the case of this post on Microsoft Community forums.
This thread, in its turn, raises other question. An independent advisory replying to the question says this is a known bug at Microsoft and the software giant is already working on a fix.
“I must tell you that the problem that occurs after the update is known and the Microsoft team is in the process of investigation, since several users have reported this incident,” the advisor posted.
The rest of the message suggests that this answer was actually referring to the data removal bug in Windows 10 October 2018 Update and not to the product key issue that the user was reporting.
For the time being, the best way to go is to create a full backup of your OS before upgrading to the October 2018 Update and to always save your product key in a secure place.

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