It is a slim possibility they got too cold. Whenever i have seen eggs freeze they usually crack. Do they always crack when frozen? I usually get to the eggs at least a few hours after they were laid and we don't get below 30F too often here and my coop usually stays about 5 F above the outside...
I too have had an egg this morning had a normal yolk with what seemed to be gooey or thicker clumps of yolk that would not mix in well. I have been searching the threads. I will test out a few more to see what happens. It was only with one hen's egg. All I can think of is that she had roundworms...