Even if you're not near max children the parent will only spawn max idle children, then it sleeps until an event, wake-up and see if more children are needed. Debug log should give some clue, if this is the reason.
Bingo. Looking further into things, it was apparent that a freshly restarted node was grossly underprovisioned WRT child processes. On intial restart, it had 5... 30 seconds later, it had 10. I manually set $loop_sleep=5 (originally hard-coded to 30) and this addressed the issue. Is this drastically smaller loop likely to have any side-effects? If not, it might be a good idea to set this upstream.
-Jared
