Recent Win 10 update KB4512941 causes high CPU usage in Cortana. This lets Cortana eat as much as 40% of CPU time when/if you disable its ability to use Bing for local searches.

Three possible work-arounds until MS fixes their latest mess...

Read here:

https://www.bleepingcomputer.com/news/microsoft/windows-10-kb4512941-update-causing-high-cpu-usage-in-cortana/