One reason why your CPU may spike after a patch reboot

I installed a new preview update to .NET and then during the subsequent boot (reboot to install updates) I noted the CPU being a little sluggish. I brought up task manager, and here’s what I saw:

Which was from this update I presume:

My understanding is that the .NET libraries are in some sort of platform independent code, that needs to be compiled to optimize it specifically for your system, so it does so in advance so your eventual use of a .NET application is not slowed.