godot: ERROR: Parent node is busy setting up children, `add_child()` failed. Consider using `add_child.call_deferred(child)` instead.

Hello! I’m making a game at Godot that plays with first-person Parkour mechanics and somehow, shortly after I messed with the resolution settings of my project, this bug started showing up in my project both in the console and in Debugger. The biggest problem with this bug is that it doesn’t allow me to open my Project Settings. Every time I try, the engine crashes. I first reported it on the Godot Facebook group, but nobody found the problem. Some users pointed out the possibility of some plugin causing this problem, but the only plugin I’m using is a Kanban plugin that I’ve had since the beginning of the project it didn’t give problems before and the problem doesn’t go away after I delete it. I haven’t found other people with the same problem, only this case (https://github.com/godotengine/godot/issues/73765) in which the same bug happens in a different way and by triggering an option that is not activated in my project. I am convinced that this is some structural bug in the engine because the more I spindle my project and all my scripts, the less I find reasons for it to happen, considering that it appears every time the game is started. Anyway, I’m sending here the code from my Main Scene, my project.godot and my global script, which are nothing big, just basic scripts to set the game menu (after all, the bug appears as soon as the engine starts, before any scene is started).

project.godot:

; Engine configuration file.
; It's best edited using the editor UI and not directly,
; since the parameters that go here are not all obvious.
;
; Format:
;   [section] ; section goes between []
;   param=value ; assign values to parameters

config_version=5

[application]

config/name="FPSTest"
run/main_scene="res://main_game_root.tscn"
config/features=PackedStringArray("4.0", "Forward Plus")
config/icon="res://icon.svg"

[autoload]

Global="*res://Global.gd"

[display]

window/size/resizable=false
window/stretch/mode="canvas_items"

[editor_plugins]

enabled=PackedStringArray("res://addons/kanban_tasks/plugin.cfg")

[input]

ui_accept={
"deadzone": 0.5,
"events": [Object(InputEventKey,"resource_local_to_scene":false,"resource_name":"","device":0,"window_id":0,"alt_pressed":false,"shift_pressed":false,"ctrl_pressed":false,"meta_pressed":false,"pressed":false,"keycode":32,"physical_keycode":0,"key_label":0,"unicode":32,"echo":false,"script":null)
]
}
ui_select={
"deadzone": 0.5,
"events": [Object(InputEventKey,"resource_local_to_scene":false,"resource_name":"","device":-1,"window_id":0,"alt_pressed":false,"shift_pressed":false,"ctrl_pressed":false,"meta_pressed":false,"pressed":false,"keycode":0,"physical_keycode":4194325,"key_label":0,"unicode":0,"echo":false,"script":null)
]
}
ui_focus_next={
"deadzone": 0.5,
"events": [Object(InputEventKey,"resource_local_to_scene":false,"resource_name":"","device":-1,"window_id":0,"alt_pressed":false,"shift_pressed":false,"ctrl_pressed":false,"meta_pressed":false,"pressed":false,"keycode":0,"physical_keycode":4194326,"key_label":0,"unicode":0,"echo":false,"script":null)
]
}
ui_left={
"deadzone": 0.5,
"events": [Object(InputEventKey,"resource_local_to_scene":false,"resource_name":"","device":0,"window_id":0,"alt_pressed":false,"shift_pressed":false,"ctrl_pressed":false,"meta_pressed":false,"pressed":false,"keycode":4194319,"physical_keycode":0,"key_label":0,"unicode":4194319,"echo":false,"script":null)
, Object(InputEventJoypadButton,"resource_local_to_scene":false,"resource_name":"","device":0,"button_index":13,"pressure":0.0,"pressed":false,"script":null)
, Object(InputEventKey,"resource_local_to_scene":false,"resource_name":"","device":-1,"window_id":0,"alt_pressed":false,"shift_pressed":false,"ctrl_pressed":false,"meta_pressed":false,"pressed":false,"keycode":0,"physical_keycode":65,"key_label":0,"unicode":97,"echo":false,"script":null)
]
}
ui_right={
"deadzone": 0.5,
"events": [Object(InputEventKey,"resource_local_to_scene":false,"resource_name":"","device":0,"window_id":0,"alt_pressed":false,"shift_pressed":false,"ctrl_pressed":false,"meta_pressed":false,"pressed":false,"keycode":4194321,"physical_keycode":0,"key_label":0,"unicode":4194321,"echo":false,"script":null)
, Object(InputEventJoypadButton,"resource_local_to_scene":false,"resource_name":"","device":0,"button_index":14,"pressure":0.0,"pressed":false,"script":null)
, Object(InputEventKey,"resource_local_to_scene":false,"resource_name":"","device":-1,"window_id":0,"alt_pressed":false,"shift_pressed":false,"ctrl_pressed":false,"meta_pressed":false,"pressed":false,"keycode":0,"physical_keycode":68,"key_label":0,"unicode":100,"echo":false,"script":null)
]
}
ui_up={
"deadzone": 0.5,
"events": [Object(InputEventKey,"resource_local_to_scene":false,"resource_name":"","device":0,"window_id":0,"alt_pressed":false,"shift_pressed":false,"ctrl_pressed":false,"meta_pressed":false,"pressed":false,"keycode":4194320,"physical_keycode":0,"key_label":0,"unicode":4194320,"echo":false,"script":null)
, Object(InputEventJoypadButton,"resource_local_to_scene":false,"resource_name":"","device":0,"button_index":11,"pressure":0.0,"pressed":false,"script":null)
, Object(InputEventKey,"resource_local_to_scene":false,"resource_name":"","device":-1,"window_id":0,"alt_pressed":false,"shift_pressed":false,"ctrl_pressed":false,"meta_pressed":false,"pressed":false,"keycode":0,"physical_keycode":87,"key_label":0,"unicode":119,"echo":false,"script":null)
]
}
ui_down={
"deadzone": 0.5,
"events": [Object(InputEventKey,"resource_local_to_scene":false,"resource_name":"","device":0,"window_id":0,"alt_pressed":false,"shift_pressed":false,"ctrl_pressed":false,"meta_pressed":false,"pressed":false,"keycode":4194322,"physical_keycode":0,"key_label":0,"unicode":4194322,"echo":false,"script":null)
, Object(InputEventJoypadButton,"resource_local_to_scene":false,"resource_name":"","device":0,"button_index":12,"pressure":0.0,"pressed":false,"script":null)
, Object(InputEventKey,"resource_local_to_scene":false,"resource_name":"","device":-1,"window_id":0,"alt_pressed":false,"shift_pressed":false,"ctrl_pressed":false,"meta_pressed":false,"pressed":false,"keycode":0,"physical_keycode":83,"key_label":0,"unicode":115,"echo":false,"script":null)
]
}
Dash={
"deadzone": 0.5,
"events": [Object(InputEventKey,"resource_local_to_scene":false,"resource_name":"","device":-1,"window_id":0,"alt_pressed":false,"shift_pressed":false,"ctrl_pressed":false,"meta_pressed":false,"pressed":false,"keycode":0,"physical_keycode":67,"key_label":0,"unicode":99,"echo":false,"script":null)
]
}
Jump={
"deadzone": 0.5,
"events": [Object(InputEventKey,"resource_local_to_scene":false,"resource_name":"","device":-1,"window_id":0,"alt_pressed":false,"shift_pressed":false,"ctrl_pressed":false,"meta_pressed":false,"pressed":false,"keycode":0,"physical_keycode":32,"key_label":0,"unicode":32,"echo":false,"script":null)
]
}
Pause={
"deadzone": 0.5,
"events": [Object(InputEventKey,"resource_local_to_scene":false,"resource_name":"","device":-1,"window_id":0,"alt_pressed":false,"shift_pressed":false,"ctrl_pressed":false,"meta_pressed":false,"pressed":false,"keycode":0,"physical_keycode":4194305,"key_label":0,"unicode":0,"echo":false,"script":null)
]
}

[physics]

common/physics_ticks_per_second=250

Main scene Script:

extends Control

@export var lastScene: String
@export var actualScene: String
@export var nextScene: String
var instanceScene

@export var loadingScene = load("res://HUD/load_screen.tscn")
var instancedLoadingScene = loadingScene.instantiate()

var gameVis
var configVis
var menuVis
var loadVis

func _ready():
	pass

func _process(_delta):
	_menuScreen()
	_pauseScreen()
	_configScreen()
	
	gameVis = Global.gameVis
	configVis = Global.configVis
	menuVis = Global.menuVis
	loadVis = Global.loadVis
	
	nextScene = Global.nextSceneToLoad
	
	if Global.loadIsReady == true:
		if $SubViewportContainer/SubViewport/GameLayer.get_child_count() == 0:
			instanceScene = load(nextScene).instantiate()
			$SubViewportContainer/SubViewport/GameLayer.add_child(instanceScene)
			Global.loadIsReady = false
			Global.gameVis = true
			Global.configVis = false
			Global.menuVis = false
			Global.loadVis = false
			$SubViewportContainer/SubViewport/Background.visible = false
		else:
			Global.loadIsReady = false
	
	if Global.isItLoading == true:
		if $SubViewportContainer/SubViewport/LoadingLayer.get_child_count() == 0:
			$SubViewportContainer/SubViewport/LoadingLayer.add_child(instancedLoadingScene)
			Global.isItLoading = false
		else:
			Global.isItLoading = false

	$SubViewportContainer/SubViewport/GameLayer.visible = gameVis
	$SubViewportContainer/SubViewport/ConfigMenuLayer.visible = configVis
	$SubViewportContainer/SubViewport/MenuLayer.visible = menuVis
	$SubViewportContainer/SubViewport/LoadingLayer.visible = loadVis

func _menuScreen():
	pass

func _pauseScreen():
	pass

func _configScreen():
	pass

func _loadingScreen():
	pass

Global Script:

extends Node

var gameVis = false
var configVis = false
var menuVis = true
var loadVis = false

var nextSceneToLoad = "res://HUD/load_screen.tscn"
var loadIsReady = false
var isItLoading = false

var pauseState = false

Plus, The error after I play the game:

Parent node is busy setting up children, `add_child()` failed. Consider using `add_child.call_deferred(child)` instead.
scene/main/window.cpp:1459 - Condition "!is_inside_tree()" is true.
Parent node is busy setting up children, `add_child()` failed. Consider using `add_child.call_deferred(child)` instead.
Parent node is busy setting up children, `add_child()` failed. Consider using `add_child.call_deferred(child)` instead.