I originally posted this question under the discussion section, but at this point I believe there may be an issue with the software or network. For the last few days I have noticed a significant increase in the processing rates even though nothing has changed with the software, proxies, or my usage of the software/server.
In general CM does not exceed a thread count of 10 with it usually below 5. Typically while in this range processing is usually in the range of 300-500 captchas/min with close to a 90% success rate. But today is the highest I've ever seen it with nearly 14,000+ captchas/min while using less than 5 threads. This amount of processing is not stable even while hosted on a large dedicated server.
I have no idea what could have possibly caused this if the software & usage has not changed and remained constant. Does CM actively communicate with your network and is it possible there could be some issue there that has led to a backlog due to some delay?
I've even tried going back to 2.10.9 which never had an issue like this, and the same problem still persisted.