Hello @Daniel Birrell
KB4012219 released on 2017 is for the older version system, and your server has already update to the newest one, so that kb is no applied for your new version now.
If you have questions about Setting up a Microsoft Defender, better open a new thread with related tag. More dedicated experts will be assigned to it.
Available Tags are here: https://learn.microsoft.com/en-us/answers/topics.html
Best Regards
Karlie
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