I'm so pleased you have put this post on as I have been searching this site for the same answer! My year old hen has also got one in the same place and keeps pecking at it. She has been sat on the nest for 26 days so I presumed it was something to do with being broody, but obviously not. Hope someone can answer us both please
My Red Stars have these spots also. I also think that most of my other ones have it also. I freaked out the first time I saw it on a girl, then I saw it on most of the girls so then I was not as worried when I saw it on more than one. To be honest I am not sure if my 2 boys have them or not. Can't pick up and hold them like my girls.