I have had a few of these so far. I gave them Poly, gave them water with a dropper, tried scrambled eggs and yogart. Nothing worked. most have died.
I have one right now doing the same thing.
But, this is JMO and might be cruel. If they fail to thrive and are weak, then I would rather not have them in my flock. I say only the strong survive. I am an animal lover and still bothers me that they die, but there is only so much one can do.
I do have one that is doing pretty gppd now, he had the same problem, but seems to have pulled out of it. So, you just never know.
I just had a Silkie SG that was dead this morning, this one really bothered me as I only had 2 anyway. But, he was not growing. His siblings were twice his size already. But, he never fell on side or anything, and he would eat, just would not grow.