You're saying either the Polish did this to each other, or somehow the much smaller d'uccles did that? Without breaking any feathers?
It certainly looks like this is what has happened. Even smaller birds and other polish can feather peck polish. I’ve certainly had it happen in my all polish flocks. Try to keep plenty in there to keep them entertained. Also some no peck spray & blue kote on the crests if they are red should help. Once started with some of them it can become a habit.