I get those from my Ameracauna a lot - every 5-10 days or so. She will drop them in the yard, at nights from the roost, and on occasion lays them in the box. We make a big pile of shavings underneath so they land gently.I was checking on the chickens this evening and I found this shell-less egg it seems , under one of the roosts. It looks like there is some kind of stuff on the bottom of it too?!
My barred rock dropped one last week during the night.
They are both 19 months old.
The other three girls, the same age - no problems.
I boil the eggs and feed them back to the girls.
Offer them oyster shell. Hopefully, it is just a one off. We have accepted that our Ameracauna will just be a bad layer.