There is a difference between the point of acquisition with pyautogui and the HSV value when reloading after saving the same image.

import pyautogui
import cv2
import numpy as np

# Set Acquisition Coordinates
x = 1000
y = 1000
width = 1000
height = 1000

# Get a screenshot
sc=pyautogui.screenshot(region=(x,y,width,high))

# Convert to np.array
sc_im=np.array(sc,dtype='uint8')

# Convert from BGR to HSV
sc_im = cv2.cvtColor(sc_im, cv2.COLOR_BGR2HSV)

# Obtain HSV maximum and minimum values
h_min_1 = sc_im.T[0].flatten().min()
h_max_1 = sc_im.T[0].flatten().max()

s_min_1=sc_im.T[1].flatten().min()
s_max_1 = sc_im.T[1].flatten().max()

v_min_1=sc_im.T[2].flatten().min()
v_max_1=sc_im.T[2].flatten().max()

hsvList1 = [h_min_1, h_max_1, s_min_1, s_max_1, v_min_1, v_max_1]
print(str(hsvList1))

# convert to RGB and save
sc=sc.convert('RGB')
sc.save("test.jpg")

# Load saved files
n=np.fromfile("test.jpg", np.uint8)
file_im=cv2.imdecode(n,flags=cv2.IMREAD_COLOR)

# Convert to HSV
file_im = cv2.cvtColor(file_im, cv2.COLOR_BGR2HSV)

# Obtain HSV maximum and minimum values
h_min_2=file_im.T[0].flatten().min()
h_max_2 = file_im.T[0].flatten().max()

s_min_2=file_im.T[1].flatten().min()
s_max_2=file_im.T[1].flatten().max()

v_min_2=file_im.T[2].flatten().min()
v_max_2=file_im.T[2].flatten().max()

hsvList2 = [h_min_2, h_max_2, s_min_2, s_max_2, v_min_2, v_max_2]
print(str(hsvList2))

 [0,176,0,255,2,255]
[0, 179, 0, 255, 0, 255]