If anyone found the answer to this I would like to know. I just had it happen..twice in a row. Same clutch. Silkie too. I'm down to two chicks and I have them in an outside brooder with a heat plate as well until I can figure it out or the grow. So far I've lost 2 in two nights and literally had to cut the feathers from the Hen they were so stuck to remove the carcasses in the morning. Never seen anything like it before but can't do it again.
Welcome to BYC!!
I'm so sorry for your loss.

I have never had this happen nor have I ever heard of this happening. Did she not pluck her underside?
None of my hens have "feathers" on their underside because they are constantly going broody. Their bottom sides are all almost bare.
If your silky mother hen isn't plucking her underside, I would trim it by an inch or two. Go all the way to nearly her butt. Maybe she was a new mom and didn't figure that part out. Next time you have one sitting on eggs, prior to hatch day I would check her to see if she plucked.
Good luck!