That's not good, I didn't see that in your last picture. Take a look and check to see if it's unabsorbed yolk and blood vessels or if it's coming from the vent and is a hernia.
If it's coming from the navel, it can possibly be saved. You're going to want to get it into a paper towel lined cup immediately so it isn't dragging that around and risking rupturing it. Then you want to make sure the incubator stays nice and humid so it doesn't dry out as it absorbs.
If it's a hernia coming from the vent, there's not much that can be done to my knowledge. In that case, it might be kinder to put it out of its misery.
It's from the vent. How do you all euthanize them?