I had this exact same problem... I was logging in on the same IP address I've used for 10 years I only managed to solve it by digging out an old phone that was

I had this exact same problem... I was logging in on the same IP address I've used for 10 years I only managed to solve it by digging out an old phone that was still signed into the Google account... if I had factory reset that then I suspect I would have lost it forever this experience is one of the many reasons I've dumped Google wherever possible