https://www.techradar.com/news/windows-10-october-2018-update-installations-could-fail-without-enough-disk-space

Microsoft is advising those with PCs that have scarce amounts of storage that the Windows 10 October 2018 Update will fail if it doesn’t have enough room to install – and that you should ensure your machine has the requisite space beforehand, because the OS won’t check for you.

In a support post addressed to devices with ‘low storage space’, Microsoft notes that machines such as thin clients or embedded systems could fail during the update initialization, and furthermore that: “Windows Update does not check systems for adequate space requirements before it initializes.”