Do prints or breakpoints, see if all is executed.
Then see if that cast does not fail. You remove something from parent.
Also you get player character right after loading level. I am not sure about this, but maybe player character is not yet loaded right after new level load.
So connect those “Cast Failed” to some print and see.
Loading a level takes some time, and the Character might not be present there so you’re getting a null reference error. Try to add a delay of some seconds and check to see if solves your issue.