It can take several days for them to come out, I have some making their way out 5 days after cutting, it happens but in the meantime I monitor them, usually you will see them moving sticking their head out etc especially in the last days.
Umbilical issues are often hard to see because of the position they are in and sadly even if you pulled the hatchling out and untangle the umbilical it's still does not guarantee that the animal will make it.
Just don't let this discourage you or give you doubt it just one of the downside of breeding things like this happens sometimes.