Chicks hatching With Large Umbilical stump protrusion/Advice Needed

[Patchesnposies]

I have an incubator full of Welsummers hatching out and I have noticed that while the yolk sac is completely absorbed there are still a couple that have a stumpy thing protruding out of their abdomen.

Any ideas on what causes this and what, if anything, I can do about it?

The babies all seem healthy otherwise.

Thanks!

Deb