I can't see anything in the photo other than what appears to be too much fluid/yolk for that stage in the development process (possibly due to a lethal failure to develop).
The only concern I would have for the umbilicus in this case would be that it was damaged while the egg was cut.
Failure of ball python egg viability in the final stages of development is common.
I would patch the egg up and continue to incubate until the snake hatches, or the egg dies.
Reply With Quote