That could be exactly why, chickens don't like change.
My first thought.
Changing the nest bedding and adding new birds will send the existing birds off to somewhere 'safer' to lay. How many 'young hens' did you add and how long ago did you add them?
Wonders if crowding is a variable here?
Dimensions and pics of coop and how many birds total might offer some clues.
You could check pelvic points to see if they are in fact laying...then you might have to figure out how to confine them...or start stalking to find that nest.
https://www.backyardchickens.com/articles/who-is-laying-and-who-is-not-butt-check.73309/