Slime Boss Spawn Issue

[Shiro2602]

I am having issue when the player enters the room and the slime boss spawns.
Godot gives me this error
"Cannot call method 'get_node' on a null value."
Which I don't get because the nodes "JumpTimer" and "Hitbox" are present in the SlimeBoss scene
I am using Godot 4.2 if this matters