It looks like a deflated soft shell egg with some egg goo attached. Do you have free choice oyster shell out for them, do you feed layer pellet?
If a chicken lays a soft shell egg, and it gets broken when she lays it, or when someone else steps on it- they will eat the yolk and whites, and leave the squishy shell. Often these will be in the nest box, but sometimes outside- they have a hard time laying them, as there is nothing to push against (too squishy), and sometimes they will be found under the perches or outside if they are walking around pushing.
I have an older girl who lays these from time to time, very annoying when she lays one on top of other nice eggs- big mess. I should cull her, as she does not give us eggs we can eat/use, but I like her too much.