In case fast startup feature is enabled, Windows 10 (and previous Windows 8 / 8.1) accomplish a partial hibernation in which the Kernel session and device drivers are saved to disk (instead of performing a cold boot in which everything has to be loaded, for example the OS kernel, applications, etc.).
When Windows is starting up, it loads up from that hibernation file, which makes boot time much faster.
This document describes how to perform a complete shutdown of the operating system for a single time and how to disable fast startup entirely. Please note, disabling fast startup is extending boot times of the operating system. However it might help to sort out or isolate unusual behaviour of the operating systes, applications or devices.