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 of hashing in spurts and stalling 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. cgminer's udev rules seem to work fine with both as far as I can tell.
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 xxx kernel: [ 10.527272] cp210x ttyUSB0: cp210x converter now disconnected from ttyUSB0
Jul 16 00:47:02 xxx kernel: [ 10.527304] cp210x 2-1.1.2:1.0: device disconnected
Jul 16 00:47:02 xxx kernel: [ 10.588515] cp210x ttyUSB1: cp210x converter now disconnected from ttyUSB1
Jul 16 00:47:02 xxx 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.