I have a suspicion, which is currently unproven, that Google may not be effectively updating their published list of Googlebot IP addresses, said Ted Kubaitis.
This suspicion arose when I recently observed some recovery on sites that had fallen in rankings.
To test this theory, I allowed non-verified Googlebots to visit my website.
Surprisingly, my site recovered within 24 hours.
While I can’t say definitively that this is the root cause of the issue, it’s something I suspect and have tried with positive results.
I want to emphasize that this is a very tentative and unproven theory at this point.
However, if you’re using solutions that rely on Google’s published IP ranges to only allow verified bots to access your website, and those solutions use that published feed, you might inadvertently be blocking valid Googlebots from visiting your site.
If you are experiencing a catastrophic loss in rankings and traffic, this is at least something you can try.