Random 401 - Unauthorized; error while loading this page error.

[Prashant Gandhi]

All, 

I'm getting randon 401 - Unauthorized; error while loading this page error. Few API request go well , and then starts giving error. I have reproduced this in a small program. Please help ! Please let me know if there is anything wrong that I'm doing, this same code has been working fine for months now. All of a sudden started giving errors since yesterday. Debugging shows that I'm getting 401 - Unauthorized; error while loading this page error at line of code which is Bold. I'm using Python 3.6.

import http.client
import json
from threading import Thread

def testing(threadname):
    loop = 0
    while loop < 100:
        loop = loop + 1
        retries = 0
        while retries < 10:
            retries = retries + 1
            try:
                conn = http.client.HTTPSConnection("XXXXXXXXXXXXXXX.atlassian.net")
                headers = {
                    'authorization': "Basic XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX",
                    'cache-control': "no-cache"
                    }
                conn.request("GET", "/rest/api/2/issue/ABC-111/", headers=headers)
                res = conn.getresponse()
                data = res.read()
                jsonstr = data.decode("utf-8")
                jsondata = json.loads(jsonstr)
                print(threadname,loop,jsondata['fields']['created'])
            except Exception as exp:
                print("Retrying ...... ",threadname,loop,retries)
                continue
            break

issuecounter = 1
thread_id = 1

while(issuecounter < 11):
    t = Thread(target=testing, name = str(thread_id),args=(thread_id,))
    t.start()
    issuecounter = issuecounter+1
    thread_id = thread_id+1