Oh, that’s awful! I buy one every week to 10 days at my local grocer; haven’t had that problem, but I always roast it in the oven for a while longer no matter what, then use my meat thermometer on it just to be sure.
Those carcasses make the BEST chicken stock. Must be all the added chemicals and hormones in them, LOL! ;)
I bought it as soon as it was out of the rotisserie, around 4 pm. They probably bank on it continuing to cook as it sits under the heater lamp. Also, the Costco chickens are HUUUUUGE!