Regarding the non-hashing or zombie units - Still using cgminer 3.7.0, I have clocked them back to 300 mhz per unit and still there would be 1-2 non hashing units that would creep up after a few minutes from initialization. The units that stop hashing are physically random (eg: first run unit 9 and 11 would stop; or second run unit 2 and 8 would stop and so forth).

edit:
I've noticed that the unit goes bad due to a usb write error. Don't know if anything came across this usb issue?

http://i.imgur.com/5UtKhyD.png

Perhaps if there is someone who is running these units with no issues, are you using a usb hub? I'm thinking the hub might be the culprit. Using Dlink 7 port usb 2.0 hub > 5 units per hub.