Earlier quoted context omitted.
It looks like it is related to authentication, landing pages seem to be working, so going incognito you can still use youtube. I would guess the search page does not actually use your credentials for anything since fingerprinting is separate from login?
I would've thought Google remembers what you search while logged in and sells it off. Maybe they do it in a different way - never really thought about that. I'm logged into Google when I search but my profile fails to load at the top right.
They probably do, but it is not essential to the functionality so it can work even if auth fails.
Fingerprinting happens separately because then they can identify you even if you are not using your own computer or are in incognito. Login is just a convenient way for you to tell them who you are.