Now I know this sounds completely ridiculous. But I might as well ask . Say my birds are sick and I have a necropsy done and they find a rare disease like newscastle. Ok should I be worried about them possibly forcibly calling my flock? Now I know this is a stretch but what do you think? my birds are not sick or anything but it's just something that came to mind.
If a necropsy found a rare disease and your birds had to be culled, I would think you should be glad in that you know the cause and you took action to prevent it spreading to other flocks. You certainly don't want your birds to suffer nor to spread that suffering to others. Later on, if you want, you can start over with a new flock.
I don't know where you got your birds, but maybe you could contact your source and ask them about any issues they are aware of with their birds. I know one local farm store here got a batch of chicks from a hatchery and they had a very bad survival rate. The store banned that hatchery after that experience, so sometimes the problem can come from the hatchery itself. The farm store wants to sell you healthy chicks so you spend lots of your good money on feed, etc.. from them as the chickens mature. Well, at least my local farm stores feel that way.
You also mentioned that you clean the coop daily. I suppose that would be a good idea, normally, but I have bought into the deep litter method. From what I have read, a deep litter bedding builds up good bacteria that is beneficial to the health of your flock. I have about 8 inches of wood chips in my coop and all I do is throw scratch on the bedding so the chickens peck and scratch the wood chips which turns the chicken droppings down into the litter. I have not cleaned out my coop in over 6 months but there is no smell at all. You would hard pressed to find any chicken droppings on their wood chip litter. It all vanishes.
I sure hope you find out why your chickens are dying. I know I would feel terrible about the situation and wonder what more could I do. I'll be following this thread so I hope you keep us updated on whatever you find out. Best wishes.