So sorry to hear about Mumbles. No guesses here.
Only hitting about 50% fertility in my Mottled Orpington pen, even though there are 2 roosters in there, so I went out yesterday and trimmed butt feathers. Those English lines have SO much fluff back there! It was pretty obvious that the feathers and caught poo on both roosters' butts were the problem. So hopefully by next week I will be getting much better fertility in there.