Hello, I didn't read the whole thread so may have missed some stuff, but I did read the entire first page.
I am again going to suggest you send hen in for a necropsy. This sounds like you have a disease running its course to me. You said the hens that started passing would have trouble standing? Maybe Mareks is an issue, that is a complete speculation though, I have 0 experience with that disease. There are so many diseases that can infect poultry, there is not a great way to guess what it is without a necropsy. You could do one yourself as well.
I know you said that your flock doesn't have a disease because you have a good breeder, and your property is clean. I'm in your same boat. Last year, my flock caught Avian Leukosis Virus as some point. Not sure if it was from a feed store, a wild bird, or the new additions I added which were from a hatchery. No way the hatchery birds had the virus, and my property is also clean, so I could have gotten it from anywhere. I lost a young pullet to it, and her passing included some suspicious symptoms. I did an at home necropsy, and then sent her into my state lab for conformation.
We both got birds from reputable sources, and don't have any contamination on our property, but its not hard to pick up poultry diseases unfortunately.
Again, I didn't read the whole thread, so I may have to play some catch up.
Did anyone rule out fatty liver disease? I see you feed Hen House Reserve. To my understanding, thats a whole grain feed correct? Whole grain feeds should be fermented or soaked to prevent picking through. The top hens will pick out their favorite seeds and leave the rest for the lower hens. That means no one gets balanced nutrition, and it causes fatty liver disease. Excessively feeding treats can be a cause as well.
I also agree that leaving out multiple full feeders 24/7 is a good idea. That will ensure everyone is getting food, and there is always food available. If your feeding a soaked or fermented whole grain feed, which you should be doing with Hen House Resever, than put out as much as you think they'll eat so that by the evening when they go to roost its gone. If it runs out anytime before that, fill it up. If you have any leftover, just add it back to the fermenting bucket at the end of the day, or put in the fridge for tomorrow.
If your feeding a dry pelleted feed, fill the feeders to the top, and leave it out until the birds roost. Then place it in the coop, or bring it into a garage at night to keep rodents from free loading.