I agree that those appear to be lash egg material, a product of oviduct inflammation and salpingitis. It can have multiple causes, but most times is from bacteria entering the oviduct from the reproductive tract or from the bloodstream. Most times lash egg material is released into the abdomen where it may be seen when butchering a chicken. Sometimes it can be passed in the droppings. Here is an article to read: https://the-chicken-chick.com/salpingitis-lash-eggs-in-backyard/