They didn’t. I saw runtime errors, like making a variable out of cast to saveGame node “saveGame instance” and then latter in code trying to get value out of that variable. Your save game BP exec node that leads to saveGame is not connected.
Good practice is that on event begin lets say HUD(any other BP will be good too)) you make a function that checks if save game exist and if it doesnt you set all values to their default and save it, thus making a save file at the start of the game. Latter you wont need to check is save game exist, you know it is there.