Nasty Egg!!!

Ok well I keep my hen on an eggshell powder(whenever she wants), lay crumble diet. She also runs out of the coop(when the run is open) and goes through the bushes, and plants, etc. Well ever since I got my chicks shes acting wierd. Shes submissive for no reason. And then today, I went to gather the egg she lay. I was shock!!! An egg with no shell. Its like if you only pull off the shell of the egg, ur left with a white soft thing, and inside are the yolk and white. Well do you know what could have caused it. And another question, can my chicks(about 9-11 weeks old) be one layer. Do the HAVE to be on grower