I would really like to hear from more people who use Circus in production. It seems interesting.
It took us a long time to trace it down and we quickly switched to runit and supervisor on a few servers. All of our problems went away.
I am interested in any form of feedback on the issues you had. Falsely detecting a work crash sounds very weird and unprobable because Circus uses the system PID list to check on processes - so I wonder what happens in your case.