This may be totally me. I haven't used GSA SER or CB in about one year. Last month I set up a few new campaigns and I'm surprised that the success rate of CB is around 15% now, when I remember it used to be around 80%. It may be that the campaigns are different (I'm only posting blog comments now, vs a number of alternatives in the previous ones). Is that it, or captcha breaker has failed to catch up with new captchas?