`ResourceGroups_List` returns different results in two consecutive calls

Testing script in python:
``` python
from azure.common.client_factory import get_client_from_cli_profile
from azure.mgmt.resource.resources.v2018_05_01 import ResourceManagementClient
from azure.mgmt.resource.resources.v2018_05_01.models import ResourceGroup
import random
import difflib
import time
import json
import requests
import subprocess

def get_subscription_id():
cmd = "az account show"
result = subprocess.check_output(cmd, shell=True)
result_json = json.loads(result)
return result_json["id"]

def get_token():
cmd = "az account get-access-token"
result = subprocess.check_output(cmd, shell=True)
token_json = json.loads(result)
return token_json["accessToken"]

def call_list_rest(subsId, token):
url = f'https://management.azure.com/subscriptions/{subsId}/resourcegroups?api-version=2019-05-01'
headers = {"Authorization": "Bearer " + token}
response = requests.get(url, headers=headers)
names = []
if response.status_code == 200:
content_json = json.loads(response.content)
for g in content_json["value"]:
names.append(g["name"])
return names

client = get_client_from_cli_profile(ResourceManagementClient)
subsId = get_subscription_id()
token = get_token()
prefix = "test"
name = f"{prefix}-{random.randint(0, 100000)}"
parameters = ResourceGroup(
location='westus'
)
group = client.resource_groups.create_or_update(name, parameters)
time.sleep(2)
names1 = call_list_rest(subsId, token)
time.sleep(2)
names2 = call_list_rest(subsId, token)
client.resource_groups.delete(name)
for line in difflib.unified_diff(names1, names2, fromfile='first', tofile='second', lineterm='', n=0):
if prefix in line:
print(line)
```
One possible result of this script of 50 consecutive executions (using `for ($i=0; $i -le 50; $i++) {echo $i; python main.py; }`):
```
0
1
2
3
4
5
6
7
8
9
10
-test-93296
11
12
13
14
15
16
17
18
19
20
21
22
-test-85758
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
-test-58905
44
45
46
47
48
49
-test-87855
50
```
It is the second list cal that always misses a resource group.

Start by running the supplied Python reproduction and compare consecutive responses from the management.azure.com resource-groups endpoint. Then inspect the repository's REST API specification coverage for ResourceGroups_List. Done means identifying the source of the inconsistent results and documenting or correcting the applicable specification behavior.

Written by the indexing model from the issue text.