Windows 10 Unistack Service Group hogging CPU to 40% or more
The Unistack Service Group is part of the Windows Store and this happens when you get App Updates. To "disable" the usage, disable the automatic App update in the Store options
and check for updates on your own and install them if you don't do work and you can ignore the higher CPU usage.
I found this is being caused by using the Mail and Calendar App in Windows 10. Stop using those and your CPU usage goes down. Need to wait for a fix from Microsoft.