You try finding the solution to what happened just now on my phone. I swiped right for my news feed only to be told “sign in for a more personalised experience”, having never signed out. Went to the sign in, found my Google account and password auto-filled – used those…”You are already signed in on this device”.
So then I attempted to look up a solution to this. Was given all kinds of irrelevant, unrelated crap. Thanks again, Google.