Same here. Windows 10, Evernote 10.15.6 (this is the newest version I've installed a few days ago, although the CPU usage problem started long before that)
It's not about one process "going berserk". The issue of insane CPU usage persists after app restart, and is replicable, such as in the following scenario:
everything seems fine as long as the Evernote app is minimized (so at least there's that)
the moment I open the window (the main app window or a single note) and my cursor lands inside a note, the Evernote process' CPU goes over 30% and my laptop starts making upset noises
it stays over 30% no matter what I do, unless...
I close all open notes and minimize the app again, then it goes down after a while
So, basically, I can't edit a note for longer than five minutes if I don't want to kill my laptop's cooling system...
EDIT: Also, sometimes the open note "freezes" (the individual note's window, or the entire main app's window, if I have it open there), and I have to minimize & show it again to unfreeze it. This seems like it may be connected to the CPU issue.