Go to https://accounts.google.com/DisplayUnlockCaptcha with the account that you are locked out of on the device. This will re-enable the access on the device you are having trouble with the Google account on.
A suspicious app might have accessed your account
Someone might have accessed your account through a suspicious app installed on this device. You've been signed out to protect your account.
Before signing in again, remove all unsafe software from this device and change your password.
To continue on this device, you'll need to verify it's you.