Python loop does not always break

I have written a loop that samples from an existing pool of images to create a (pseudo-)randomized list. The goal is to have a list where the images appear a specific number of times but without consecutively repeating the same image.

I have tried the following code:

import random

number_img1 = number_img2 = 2
number_img3 = number_img4 = 4
number_img5 = number_img6 = 6

total_images = number_img1 + number_img2 + \
    number_img3 + number_img4 + number_img5 + number_img6

stimulus_full_random = []
new_item = 0

while len(stimulus_full_random) < total_images:
    new_item = random.choice(stimulus_full)
    if len(stimulus_full_random) == 0:
        stimulus_full_random.append(new_item)
    elif 0 < len(stimulus_full_random) < total_images:
        if new_item == "img1_full" and stimulus_full_random.count("img1_full") < number_img1:
            if new_item != stimulus_full_random[-1]:
                stimulus_full_random.append(new_item)
            else:
                stimulus_full_random[-1] = new_item
        elif new_item == "img2_full" and stimulus_full_random.count("img2_full") < number_img2:
            if new_item != stimulus_full_random[-1]:
                stimulus_full_random.append(new_item)
            else:
                stimulus_full_random[-1] = new_item
        elif new_item == "img3_full" and stimulus_full_random.count("img3_full") < number_img3:
            if new_item != stimulus_full_random[-1]:
                stimulus_full_random.append(new_item)
            else:
                stimulus_full_random[-1] = new_item
        elif new_item == "img4_full" and stimulus_full_random.count("img4_full") < number_img4:
            if new_item != stimulus_full_random[-1]:
                stimulus_full_random.append(new_item)
            else:
                stimulus_full_random[-1] = new_item
        elif new_item == "img5_full" and stimulus_full_random.count("img5_full") < number_img5:
            if new_item != stimulus_full_random[-1]:
                stimulus_full_random.append(new_item)
            else:
                stimulus_full_random[-1] = new_item
        elif new_item == "img6_full" and stimulus_full_random.count("img6_full") < number_img6:
            if new_item != stimulus_full_random[-1]:
                stimulus_full_random.append(new_item)
            else:
                stimulus_full_random[-1] = new_item
    else:
        break

print(stimulus_full_random)

In some cases, it produces the desired output but sometimes, the loop does not break / the program runs on forever. I have tried several different versions, but always the same result. I am fairly new to programming and I do not understand why (only in some instances) this code does not work. Help is very much appreciated!