Noticed a lot of false positive too since the new year.
After investigation, it appeared that the ahbl.org's RBL was now wildcarding everything as spam : http://ahbl.org/node
In my particular case I use my own servers that flags mails before sending them to google.
I doubt that google relies on ahbl but most servers with a old version of spamassassin do.
IMHO Those false positive by gmail might be due to a large amount of false positive forwarded to them by servers that rely on spamassassin.
After investigation, it appeared that the ahbl.org's RBL was now wildcarding everything as spam : http://ahbl.org/node
In my particular case I use my own servers that flags mails before sending them to google. I doubt that google relies on ahbl but most servers with a old version of spamassassin do.
IMHO Those false positive by gmail might be due to a large amount of false positive forwarded to them by servers that rely on spamassassin.