c1iscex is back up. It is communicating with it's IO chassis, and all of it's models (c1x01, c1scx, c1spx) are running again.
The problem was that the IO chassis had no connection to the computer. The One Stop card in the IO chassis, which is the PCIe bridge from the front-end machine and the IO chassis, was showing four red lights instead of the dozen or so green lights that it usually shows. Upon closer inspection, the card appeared to be complaining that it had no connection to the host card in the front-end machine. Un-illuminated lights on the host card seemed to be pointing to the same thing.
There are two connector slots on the expansion card, presumably for a daisy chain situation. Looking at other IO chassis in the lab I determined that the cable from the front-end machine was plugged into the wrong slot in the One Stop card. wtf.
Did someone unplug the cable connecting c1iscex to it's IO chassis, and then replug it in in the wrong slot? A human must have done this.