Any new layers in your group? What is their age, how many total chickens? What do you feed including treats?
How long has your silkie been laying yolk free eggs? Sometimes soft shelled eggs can be a sign of the reproductive system starting up or shutting down. Some times there are just hiccups. And sometimes they may never become normal.
When you found that... in the box or somewhere else?
When I say starting or stopping, I just mean their normal cycle, not permanently.
I was thinking more along the lines of starting back up after coming out of molt since they are that age and it's that time of year. Here is an article that is at least an interesting read and does talk about your silkie eggs as well...
Before long your head will be spinning with so much chicken info you might accidentally say "bok bok"! No, I'm just kidding. But this is a great and helpful community where almost any chicken question can be answered. If you're like the rest of us though... you probably lurked for a while before signing on and already know that!
Enjoy BYC, and have a great time becoming part of the family!