Image Subscriber Lags (despite queue_size=1 and buff_size=2**30)

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Hi,

I have been working on a Python class that will allow me to spawn an object in gazebo, take an image of the object, and then delete that object, for a given number of objects that I provide. I am able to spawn the objects, and have written a subscriber that is able to take images using a sensor. However, the images that are saved are not being taken in the order I am asking them to. Starting the script, I seem to be getting images out of order. For example, if I set it to spawn 5 objects without deleting for clarity, and take an image each time a new object is spawned, I could have 1 image without any objects, 3 images with 2 objects present, and the last image with 3 objects present. Sometimes I even get images with objects in positions that were set the last time I ran the script.

I thought this was because my publisher and subscriber were working at different rates, so looking at the answers on this forum I added queue_size=1 and buff_size = 2***30, to make sure that it was taking the last image that was sent. However, the problem is still there and nothing has changed. I have also tried increasing the time delay which has not helped, and was trying to find a way to delete the subscriber queue each time so that the latest message was definitely the one being read, but I have been unable to do so. I am not sure how to solve this and was wondering if anyone had a solution to this or an idea of why this was happening? I have attached my code below. Thanks!

import numpy as np
import rospy, tf, time
from gazebo_msgs.srv import SpawnModel, DeleteModel, GetModelState
from geometry_msgs.msg import *
from take_photo import ImageNode
# ROS Image message
from sensor_msgs.msg import Image
# ROS Image message -> OpenCV2 image converter
from cv_bridge import CvBridge, CvBridgeError
# OpenCV2 for saving an image
import cv2
import os

class ImageCollection():
    def __init__(self, number_spawn, model_path, time_delay=3.0):
        print("Waiting for gazebo services...")
        #rospy.init_node("spawn_products_in_bins")
        rospy.wait_for_service("gazebo/delete_model")
        rospy.wait_for_service("gazebo/spawn_sdf_model")
        rospy.wait_for_service("gazebo/get_model_state")
        print("Got it.")
        self.delete_model = rospy.ServiceProxy("gazebo/delete_model", DeleteModel)
        self.spawn_model = rospy.ServiceProxy("gazebo/spawn_sdf_model", SpawnModel)
        self.model_coordinates = rospy.ServiceProxy("gazebo/get_model_state", GetModelState)

        # Instantiate CvBridge
        self.bridge = CvBridge()
        self.image_number = 0
        self.number_spawn = number_spawn
        self.time_delay = time_delay
        self.model_path = model_path

        # Create a directory to store images
        self.folder_path = "Gazebo_Images"
        try:
            os.mkdir(self.folder_path)
        except:
            print("Folder already exists, appending to that folder...")

        # Initialize the node
        rospy.init_node('image_listener')
        # Define your image topic
        self.image_topic = "/wamv/sensors/cameras/front_left_camera/image_raw"
        # Set up your subscriber and define its callback
        # rospy.Subscriber(image_topic, Image, self.image_callback)
        # rospy.spin()

    def spawn(self):

        with open(self.model_path, "r") as f:
            product_xml = f.read()

        # Determine a random position for the buoy (function has not been shown here but is just a random generator)
        bin_x, bin_y ...