Well, it's clear that you care about your chicks, chickens and ducks a lot. When you put up photos of them they are always in good condition and healthy looking. I think you are a responsible owner.
Sometimes chicks die. I know plenty of responsible owners who are also very experienced and who breed a lot and still suffer major losses from time to time. Chicks are vulnerable to a lot of things that can make them sick. Probably the main thing is coccidiosis, which I'm sure you know. If a chick gets sick then the first thing I'd do is treat with something that will deal with the cocci. I use Baycox, because that kills the things that cause the problem (whereas other things tend to just slow them down). So that's my only advice, if you are not already treating them for cocci.
Just because you have had a bad run with chicks lately doesn't mean you are doing anything wrong or are not responsible. If they have enough space, a clean environment, heat, fresh water and appropriate care and/or medication when they are sick then you are giving them everything they could need and you are doing everything that a person could do.
