The first PoseStamped msg publish to /move_base_simple/goal is not working

Question

I have a simple python program trying to publish 2 points stored in a list in sequence, but i have noticed that the first point being published has no effect. But if i publish a 2D Nav Goal in RViz, the car starts moving, soon it reached the goal, which the program is listening to the move_base/result， it soon publish the second point and the car starts moving as well.

So i was wondering why the car won't move when the first point is being published? I can confirm that the movebasesimple/goalget the first PoseStamped msg.

Here is the code:

#!/usr/bin/env python

import rospy
from visualization_msgs.msg import Marker
from geometry_msgs.msg import  PoseStamped, Twist
from move_base_msgs.msg import MoveBaseActionResult, MoveBaseAction
from actionlib_msgs.msg import GoalID
import actionlib
from static_points import StaticPoints

class MultiNavServer:
    def __init__(self):
        self.points = StaticPoints().get_points()
        self.point_index = 0
        self.is_car_ready = True
        self._rate = rospy.Rate(10)

        self.pub_goal = rospy.Publisher('move_base_simple/goal', PoseStamped, queue_size=1)
        self.pub_cancel_goal = rospy.Publisher('move_base/cancel', GoalID, queue_size=1)
        self.sub_goal_result = rospy.Subscriber('move_base/result', MoveBaseActionResult, self.goal_result_callback)
        self.pub_cmd_vel = rospy.Publisher('cmd_vel', Twist, queue_size=1)

    def shutdown(self):
        self.pub_cancel_goal.publish(GoalID())
        self.pub_cmd_vel.publish(Twist())
        rospy.loginfo("Shutting down multi_nav_server")

    def send_goal(self):
        self._rate.sleep()
        goal = PoseStamped()
        goal.header.frame_id = 'map'
        goal.header.stamp = rospy.Time.now()
        goal.pose.position.x = self.points[self.point_index].pose.position.x
        goal.pose.position.y = self.points[self.point_index].pose.position.y
        goal.pose.orientation.z = self.points[self.point_index].pose.orientation.z
        goal.pose.orientation.w = self.points[self.point_index].pose.orientation.w
        self.pub_goal.publish(goal)
        # print("Publishing goal" + str(self.point_index) + ":\n" + str(goal))
        self.is_car_ready = False
        self.point_index += 1


    def goal_result_callback(self, msg):
        print("Goal reached, setting car ready...")
        self.is_car_ready = True
    
    def run(self):
        rospy.on_shutdown(self.shutdown)
        while not rospy.is_shutdown():
            self._rate.sleep()
            if self.is_car_ready and self.point_index >= len(self.points):
                print("All stations reached, shutting down...")
                break
            if self.is_car_ready and self.point_index < len(self.points):
                print("Sending point" + str(self.point_index) + "...")
                self.send_goal()
            self._rate.sleep()

if __name__ == '__main__':
    try:
        rospy.init_node('multi_nav_server_static')
        multi_nav_server = MultiNavServer()
        multi_nav_server.run()
    except rospy.ROSInterruptException:
        pass

The terminal output is:

Sending point0...
Goal reached, setting car ready...
Sending point1...
Goal reached, setting car ready...
All stations reached, shutting down...
[INFO] [1688739930.946100, 5529.329000]: Shutting down multi_nav_server

What happened above, is the program hangs at Sending point0..., I have to manually set a 2D Nav Goalin Rviz, soon after the goal is reached, the program send point1 and the car is moving as normal.

I was running a simulation through Gazebo, the /use_sim_time is set to true...

What is the logic behind my bug??

Edit: I have found that the /move_base_simple/goal and /move_base/goal should have similar msgs being published. Like when i publish a 2D Nav Goal in Rviz, both topics get the same target goal location. With this being said, the first location published from my program, is only being published to /move_base_simple/goal but the second one is publishing to both topics. I think this may be the problem. How do i fix this?

thx in advance!