Neons used to be a hardy fish until they started breeding them in the same water so they wouldn't adapt. After a little while as they couldn't adapt as well as wild neons they sometimes would find it hard adapting to other fish tanks. Thus why they die so easily.
Fish that die are free food. They will go for the eyes as they are the best?
I'd come home one day and say my 2 kuhli loaches eating a dead fishes stomach. Weird stuff.
My new tank is going ok. Only got a male betta n 2 kuhli's. Should be moving the Betta out n getting some molly fry.