Not an error, but a change in the Windows 2012 AMI configuration.
You used to be able to add ephemeral volumes, but it was unclear how much you could add. Now, to “fix” it, they put them all down to show how much you have, and then you delete the ones you don't need. those. - in most cases - all of them.
I'm not sure if this is a particularly good change, but this is the answer I received from the support.
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