Turn off hibernation/fast startup. For some reason, they kick in even on an SSD Boot system, resulting in the system not shutting down entirely but saving files for preloading on the next boot.
Preloaded files/content don't show up in the task manager. But still, take up space, so they get accounted for in the total ram used even.
Also, Superfetch (SysMain) will preload files to ram but now show up as if they are there.