I've had a similar problem with cgminer 3.3.2
There's a 3.3.2? I'm still using 3.3.1, which is working great for me with USB Erupters. Of course I only have 15 of them with USB 2.0 Hubs.
Opps I think I meant 3.3.1, but mostly I meant latest master from github (805672fb51f4219e8c5848dc761509d32bffde9f -- I think it identifies itself as 3.3.2, sorry I forgot it wasn't released yet). I tried master from github first when I couldn't get 3.3.1 to work. I was about to blame the hub when I decided to try building 3.1.1 as a hail mary.
They're still working on the USB 3.0 Hub support. Which was the reason I bought USB 2.0 Hubs.
Glad your working at least.
Sam
For me USB 3.0 hubs do not work in USB 3.0 slots, but if I plug them into USB 2.0 slots they work fine. It might be worth a try if you already have the hardware.
Oh, right. I forgot to mention that I excluded the hub as the problem before going to 3.1.1 by reproducing the findings with the USB Eruptors plugged in directly to the computer. I observed the same behavior where individually they work fine but if two were installed each device would mine for a bit and then enter into some sort of standby mode with solid leds (they don't both enter that state at the same time--one will get there sooner than the other). Then after a few seconds both will start hashing again simultaneously. That pattern just keeps repeating itself. I didn't time it but my guess is ~15-30sec. The computer itself is an Celeron-based Intel NUC that only has USB 2.0 ports.
I don't know if it matters but the the second miner came from BTCguild and was "branded" (I assume via the Luke-JR method) but the first comes from CanaryInTheMine and is unbranded. The udev rules didn't care.
Looking back through the logs did finally notice one thing. When running the 3.2.x or github version, this happens once per reboot when cgminer is starting up:
Jul 16 00:47:02 ohms kernel: [ 10.527272] cp210x ttyUSB0: cp210x converter now disconnected from ttyUSB0
Jul 16 00:47:02 ohms kernel: [ 10.527304] cp210x 2-1.1.2:1.0: device disconnected
Jul 16 00:47:02 ohms kernel: [ 10.588515] cp210x ttyUSB1: cp210x converter now disconnected from ttyUSB1
Jul 16 00:47:02 ohms kernel: [ 10.588549] cp210x 2-1.1.4:1.0: device disconnected
When this happens /dev/ttyUSB0 and /dev/ttyUSB1 disappear and never return. But cgminer 3.2.x is still able to hash in spurts. I had to reboot to get 3.1.1 to work.
3.2+ is doing that. It no longer uses the ttyUSB devices so it removes them to disable the driver so that cgminer can use raw USB through libusb.