The update has finally a bug in Task Manager that causes incorrect reporting of CPU usage. It’s one of the known issues that Insiders reported during the testing of October 2018 Update but for some reason, it wasn’t fixed before the public launch. […]

from https://www.bleepingcomputer.com/news/microsoft/windows-10-october-2018-update-build-17763104-released-to-insiders-with-fixes/