Google may be crawling the web with a new crawler, a new Googlebot, named GoogleProducer. This useragent is not listed on the official Google crawlers page but maybe it is too new to be listed yet?
Hernán Marsili spotted this and asked Google about this on Twitter. He said, "we are seeing a lot of traffic to publisher's sites with a new user-agent 'GoogleProducer; (+http://goo.gl/7y4SX) '. Our WAF is currently blocking it, but it's origin is actually Google Proxy hosts. Is this legit traffic?"
That link goes to this page that 404s within the Google News Producer section.
As an FYI, Google Producer is part of Google News and Google Currents, I believe. This help document from Google says, "You will use Google Currents producer to manage your issues (e.g., pricing, description, etc.) for Google Play Magazines. If you're participating in Google Currents, Producer will look familiar to you. You can manage both your edition(s) for Google Currents and your issues for Google Play Magazines through Producer. See our article on publisher account setup for the steps you need to take to fully set up your publisher account and magazines for Play. If you have any questions about using Producer for Google Currents, please see the Currents Producer Help Center." Note, the Currents Producer Help Center redirects to the Google Publisher Center help center.
John Mueller of Google said he will look into it:
I'll check - thanks for pinging.
— John Mueller is watching out for Google+ 🐀 (@JohnMu) February 1, 2023
I guess we will see what he says but until then, I do suspect this is a legit Googlebot crawler.
Update: This is old, an older one:
2011 on this thread?https://t.co/NTqpOhQYSl
— Pedro Dias (@pedrodias) February 2, 2023
Forum discussion at Twitter.
Update: February 10th Google added it to the list of supported Googlebots.