About a month ago when my Muscovies were hatching, they had pipped their shells and did not make any progress for over 24 hours. I eventually decided to help the hatching process. It turns out that the membrance just under the shell had turned to a rubbery-like membrane, through which they could not progress.
I started picking away small pieces of the shell to expose the membrane, then started peeling away the outer membrane. If it looked as though they were bleeding, I would stop for several minutes to let the bleeding stop, then continue. I only had 1 chick die, although I don't think he would have made it anyways.
Hope this helps, and good luck!
Cheers
Allie