If you have a Google account error that says "something has changed" and asks you to log in again, there's no cause for alarm. Google tells us they know something's up and it's not related to any suspicious activity.
We've gotten reports about some users being signed out of their accounts unexpectedly. We're investigating, but not to worry: there is no indication that this is connected to any phishing or account security threats.
Please try to sign-in again at accounts.google.com and if you cannot remember your password, please use this link (g.co/recover) to recover your password. If you use 2-Step Verification, there may have been a delay in receiving your SMS code. Please try again or use backup codes.
OK, cool. Nobody is trying to get into our email accounts, but signing in again isn't as easy as they make it sound. If whatever is going on glitches your account, all the things logged in with that account can be royally hosed and need to be set up or attached to your account again.
We know Google Wifi went crazy for some users earlier, and they tell us there were "issues with the Google Accounts Engine today" which caused problems, and that could be tied into whatever is happening with Gmail, Google Home, and Chromecasts that are being reported as not working tonight, but Google hasn't said anything just yet.
We're happy that it's not a security thing, but it's still a thing if you're one of the unlucky people affected. For now, you can follow the advice and log-in again from your phone or computer. Hopefully, Google tells us more if only to satisfy our curiosity.