Huh. I don't use #Google accounts for much but I'm sure glad I don't since it seems locking random devices out of logging in for some months is a normal way of working for them.

<device suddenly asks to log in again>
<fill in extra information as requested from all the recovery contacts, which is not sus at all I guess>
"Sorry we just can't be sure it is you."

<logs out explicitly from an insecure old Android device>
<tries to log back in for comparison>
"Oh it must be you hello welcome back! Would you want to offer security codes for other devices? We won't accept them anyway but we can still demand to see them!"

Goodbye, Pokemon Go, it was fun while it lasted. I will now be focusing on playing #Walkscape then I guess.

Also public service announcement: Niantic has gotten better at supporting other accounts, so you will want to link an actual stable non-Google login method to your games if you can still get in.

Sadly Pokemon Trainer Club is not known for being particularly stable. X-) But sounds like Apple IDs might be reasonably ok if applicable to your situation.