Soft, light colored egg after normal eggs

My barred Plymouth Rock has been laying for two weeks. She's been laying 4 days on 1 day off. She just took a two day break for the first time and today her egg was much lighter in color, almost white, and the shell was very thin. She also seemed to be in the nest box longer. I have oyster shell free choice in the coop, and it doesn't seem like calcium deficiency could crop up that quickly anyway after a bunch of normal eggs.

I have been switching them over from a mix of grower crumbles and layer pellets (only one pullet is currently laying), to a whole grain based ration with a high protein supplement. Its between 16% and 17% protein in the proportions I am mixing and is formulated to have all the essential vitamins and minerals. They free range several hours a day as well, and have access to fresh pasture in their tractor all day. Treats are limited to garden gleanings and kitchen scraps. Right now mostly pumpkins, tomatoes, and peppers.

Should I not worry about this and just chalk it up as her working the kinks out, or could it be indicative of a larger problem?

Thanks!!