Its definately not water temp, ive pulled crays from freezing water and dropped them in my tanks and they are not effected
i say stress, one time i took a full grown cray out of my tank, he was killing too many of my fish, clipped off one half of his large pincher with a sizzors, dropped him back in the tank, he rolled up in a ball on the way to the bottom of the tank and layed there, i thought he was playing dead, came back like an hour later and he was still in the ball, dead fur real.
Have done this too numerous rogue crays, i like them to scavange on the bottom and clean up after my piranha, have also had some die during molting, i think they are cool little critters
they are escape artists, be sure your tank is sealed up, they will surprise you