I doubt this has anything at all to do with the pool. Anything to do with those would affect both USB devices.
If anything I'd guess it somehow lost power for a while. I don't know anything about pi's, are they running on a powered hub or direct? If they are on a hub maybe the wall-wart is on it's way out.
There weren't any errors showing up when you restarted cgminer were there? I'd imagine you would have mentioned that though...
if it happens during a submit or request the erupters act weird when it happens to mine it normally just reports a com error and locks the erupter up with a solid green light. the only way to get it to mine again is unplug the erupter and plug it in again
Weird. I quit using cgminer for bfgminer, but occasionally I see one of mine go solid but it always rights itself automatically. I imagine it turns back off on the next submitted share, but I've never cared enough to check.
Either way, with BFGminer I've been up for 2 days, 7 hours and 56 minutes and all 10 are within around 100 shares of each other, haven't had to touch them. I've gone longer, but do you have that problem more frequently than this? Might be worth changing maybe.
Hah, one just did it now! Silly eruptors