Level blueprint, GameMode blueprint, general blueprint, and so on.
What is the order of execution of blueprint on every frame?
GameMode blueprint whether instead Level blueprint?
Just go into each of them and add a print string to each one of them, and then play the game and quickly stop it, then go look at the output log to see what order they fired in.
On game load, game mode will load first because it is going to tell the game what level and player controller to use. I am not sure what order game mode loads the rest though. I am assuming level, player controller, then player.
During runtime, they will execute in whatever order you specify.