Please note that my Godot version is 3.3 so that could be a reason.

I tried to create a script to shoot bullets.

First I tried using the input function

func _input(event):
    # Mouse in viewport coordinates.
    if event is InputEventMouseMotion:
        #print("Mouse Motion at: ", event.position)
        look_at(event.position)
    if event is InputEventMouseKey:
        direction = event.position
        print("Mouse Click/Unclick at: ", get_global_mouse_position())
        var shoot = bullet.instance()
        get_parent().add_child(shoot)
        shoot.global_position = global_position
        yield(get_tree().create_timer(0.08), "timeout")

Then I tried using event.isEcho() and a state (also used Input.is_just_pressed())

enum {
IDLE
SHOOTING
}

Here is my current code: Sprite code (player/gun)

extends Sprite

onready var bullet = preload("res://bullet.tscn")
onready var direction = null

var pos = null

# Called when the node enters the scene tree for the first time.
func _ready():
    pass

func _process(delta):
    if Input.is_action_just_pressed("click"):
        direction = get_global_mouse_position()
        print("Mouse Click/Unclick at: ", get_global_mouse_position())
        var shoot = bullet.instance()
        get_parent().add_child(shoot)
        shoot.global_position = global_position
        yield(get_tree().create_timer(0.08), "timeout")

func _input(event):
    # Mouse in viewport coordinates.
    if event is InputEventMouseMotion:
        #print("Mouse Motion at: ", event.position)
        look_at(event.position)

Bullet: (not so relevant as my question is why process and input runs twice)

extends KinematicBody2D

var direction = Vector2.ZERO
var MAX_SPEED = 20
var ACCELERATION = 5
var velocity = Vector2.ZERO

onready var tween = $Tween

func _ready():
    direction = mouse.direction
    # (81, 23)
    tween.interpolate_property(self, 'position', position, direction, 0.8, Tween.TRANS_LINEAR, Tween.EASE_OUT)
    tween.start()
    yield(get_tree().create_timer(0.8), "timeout")
    queue_free()
```