When things start acting up, it helps to start looking at all of the links in the chain. I first looked at RAM and that made me think about using disk utility to look at my drives: the OS / Applications first, then the main storage device ( a 4 bay Drobo V2) and then my second Drobo that I use for time capsule, Lr backup and as a scratch drive. And the second Drobo is where the problem apparently was: one of the older drives in it (3 years?) was flash ing red in the Drobo Dashboard and on the front of the enclosure which is under my desk. Swapping the bad drive out for a new one either solved the problem or the problem cleared up simultaneously.