Sorry, about not being clear... here is what I do.
I usually buy 4 dozen eggs (in plastic cartons). I do store them on the bottom shelf of my refrigerator by the side wall. I sometimes start a new dozen before using all of the eggs in the first dozen. So this problem has been relatively new, and, inconsistent.
This problem has occurred with some eggs over the last 2 weeks, probably in more than one carton - but I have no way of being certain.
I crack all of my eggs on the counter.
I separate them with my hands, which made me feel the lumpiness. When this problem happens, "gelatinized" or "very thick" would be a good way to describe the yolk.
I think you may have figured out the problem here! I'll try to store my eggs in a warmer spot.