Then it was just a glitch. Personally I never worry about double yolks in eggs. My boys always thought they were lucky! But it is a common egg glitch, and as far as I can tell in decades of chickens - harmless.
I really don't worry about soft-shell eggs either. They are what they are. Tend to be a mess. They tend to clear up in 7 days if you treat them, and a week if you don't.
In fact, I am beginning to think I don't worry about a lot of things, as I just cook with my eggs, and toss the shells into the chicken scrap bucket. Never had it make a difference.
The egg lash egg would make me worry. I would cull that bird. That signals a major infection. I don't want that bacteria in my coop and run. So are you positive that is what you had?
As for me, if a bird is active, bright eyed and lively, I don't worry about them. They are doing fine. They can have egg laying glitches, but I don't think it has much to do with diet, unless your diet is severely short of calcium. Egg laying is much more a genetic issue. I would not hatch eggs of the birds that were worrying you.
I have never given a calcium pill. Mine seem to thrive on healthy neglect.
Mrs K