[HELP] Severe Lag Spikes problem

Here's a BEFORE and AFTER video below
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I couldn't really track what really just happened. It occured after putting resources of every nodes needed, bullet nodes, shooter nodes, enemy nodes, etc. However, I tried reverting them back but none of them are solved.

here are the current codes below:

bullet code:

class_name BulletClass

export var bulletRes: Resource


func _die() -> void:
	set_deferred("monitoring", false)
	bulletRes.spd = 0
	rotation = 0
	$AnimatedSprite.play("die")
	yield($AnimatedSprite, "animation_finished")
	queue_free()

#func _move(delta) -> void:
#	position += bulletRes.dir * bulletRes.spd * delta
#	bulletRes.spd += bulletRes.changingSpeed * delta

func _cancel() -> void: 
	if !bulletRes.cancelled:
		bulletRes.cancelled = true 
		$scoreManager._spawn_gems()
		_die()


func _ready() -> void:
	$AnimatedSprite.play("default")
	if bulletRes.rotate: rotation = bulletRes.dir.angle()


func _on_VisibilityNotifier2D_screen_exited() -> void: queue_free()


func _on_bullet_area_entered(area) -> void:
	if area is Enemy: area._damage(bulletRes.damage)
	elif area is Hurtbox: area._dead()
	
	_die()

shooter code:

class_name Shooter

export var shooterRes: Resource

var bullets: Array = []


func _timer() -> Timer: return get_node("Timer") as Timer

func _shoot(lookAtPos: Vector2 = Vector2.RIGHT) -> void:
	if $Timer.is_stopped():
		$Timer.start(shooterRes.fireRate)
		
		for i in shooterRes.arcRepeat:
			if owner is Enemy:
				if !owner.enemyRes.canDamaged or owner.player.dead: 
					$Timer.stop()
					break
			
			var b = shooterRes.bullet.instance() as BulletClass
			
			if shooterRes.staticDirection: $Position2D.rotation = Vector2.RIGHT.angle_to(lookAtPos)
			else: $Position2D.look_at(lookAtPos)
			
			b.global_position = $Position2D.global_position
			
			if shooterRes.arcRepeat != 1:
				var arcRad = deg2rad(shooterRes.arc)
				var inc = arcRad / (shooterRes.arcRepeat - 1)
				$Position2D.rotation += inc * i - arcRad / 2
			
			b.bulletRes.dir = Vector2.RIGHT.rotated($Position2D.rotation + shooterRes.customRotation)
			
			if shooterRes.customSpeed != 0: b.bulletRes.spd = shooterRes.customSpeed
			
			b.bulletRes.changingSpeed = shooterRes.changingSpeed
			
			get_tree().root.call_deferred("add_child", b)
			
			bullets.append(b)
			
			rotation = 0



func _physics_process(delta) -> void:
	if bullets.empty(): return
	
	for bullet in bullets:
		if is_instance_valid(bullet): 
			bullet.position += bullet.bulletRes.dir * bullet.bulletRes.spd * delta
			bullet.bulletRes.spd += bullet.bulletRes.changingSpeed * delta
		else: bullets.erase(bullet)

somewhere between them are the fault I really couldn't tell but help is super appreciated