Eggs with blood in them

[Barbyka]

I just recently got into chickens, and a neighbor told me the last packet of 10 had 4 like that inside. I still have no explanation as to why that happens. I get the 10 eggs per day, so that means 4 chickens had similar problem at the same time. Can it be food? I recently added a new outdoor space, so maybe some plants/bugs? And one difference is that she said the yolk was runny. Not smelly, no meat spots, no embryo. Just runny yolk with some blood.