Sticks just start dropping out into zombie. Cpu is at 85%. I'm only using usb 2.0 and tried running the third hub off of one of the other two and that didn't help. Still can't go over 10 sticks.
That's the same exact issue I have had. I remedied it by using only half the hub, but my hubs are 30 slots each. Read up on that link I sent above, pull up USB tree and see what chips are used in the hub and how many hubs system sees there. I would also try to completely reinstall the Raspbian and Cgminer (30 min) and start over from clean setup.