I think it's just time for "stuff" to happen. The first years were trouble free except for that pesky bumblefoot thing and now, it's time to pay the piper, I guess. At least, none of this is anything contagious, which would be infinitely worse! My older girls are just getting on up in age now, although they aren't old to me, and they've been fantastic layers all the way along, even through winter. Maybe they're paying for it now, who knows? No matter how well you manage your flock, there will be losses like this if you own chickens long enough and now is my turn, I expect. Knowing that doesn't make it easier, though.