`az network vnet list -g rg_name` returns different results when executed on different machines

**Describe the bug**
The command `az network vnet list -g {rgName}` sometimes repeatedly returns incorrect value (empty array, `[]`).
The same command executed on another machine at the same time for the same resource (e.g. from Cloud Shell in Azure Portal) returns correct, non-empty result.

**To Reproduce**
This might be complex to reproduce in practice. I think that the correlation ids from logs might be more useful. But the scenario is:
1) Deploy AKS cluster using ARM template. Set the parameter `nodeResourceGroup` to some unique value, eg. `resourcegroup-123`.
2) Shortly after the cluster is deployed, run `az network vnet list -g resourcegroup-123`
3) The response often is empty array `[]`, even if virtual network already exists and is accessible from other instances of `az cli` or Azure Portal.
4) Retry several times. The response can often be `[]` for 40 minutes of retries or longer. Then it can start responding properly, or our pipeline times out.

**Expected behavior**
The command should return the same list of virtual networks in the resource group, regardless of the instance of `az cli` we're using to issue query.

**Environment summary**
- Azure Pipelines using AzureCLI@1 task.
```
azure-cli 2.20.0
core 2.20.0
telemetry 1.0.6
Extensions:
azure-devops 0.18.0
```

**Additional context**
I ran `az network vnet list -g {rgName} --debug` (with the `--debug` parameter). Here is the interesting part that shows the response is insonsistent across clients:

Output from Azure Pipelines:
```
(...)
DEBUG: azure.core.pipeline.policies._universal: Request URL: 'https://management.azure.com/subscriptions/ec0308fb-8d6e-497a-9dd6-99c7d9ab7962/resourceGroups/unicorn-dev-euw-aksresources-rg/providers/Microsoft.Network/virtualNetworks?api-version=2020-08-01'
DEBUG: azure.core.pipeline.policies._universal: Request method: 'GET'
DEBUG: azure.core.pipeline.policies._universal: Request headers:
DEBUG: azure.core.pipeline.policies._universal: 'Accept': 'application/json'
DEBUG: azure.core.pipeline.policies._universal: 'x-ms-client-request-id': 'ffc98a5f-830f-11eb-bcd3-49af26ce1415'
DEBUG: azure.core.pipeline.policies._universal: 'CommandName': 'network vnet list'
DEBUG: azure.core.pipeline.policies._universal: 'ParameterSetName': '-g --debug'
DEBUG: azure.core.pipeline.policies._universal: 'User-Agent': 'AZURECLI/2.20.0 (DEB) azsdk-python-azure-mgmt-network/17.1.0 Python/3.6.10 (Linux-5.4.0-1040-azure-x86_64-with-debian-bullseye-sid) VSTS_4aa70140-adae-4225-af61-2e88983101cc_build_670_0'
DEBUG: azure.core.pipeline.policies._universal: 'Authorization': '*****'
DEBUG: azure.core.pipeline.policies._universal: Request body:
DEBUG: azure.core.pipeline.policies._universal: This request has no body
DEBUG: urllib3.connectionpool: Starting new HTTPS connection (1): management.azure.com:443
DEBUG: urllib3.connectionpool: https://management.azure.com:443 "GET /subscriptions/ec0308fb-8d6e-497a-9dd6-99c7d9ab7962/resourceGroups/unicorn-dev-euw-aksresources-rg/providers/Microsoft.Network/virtualNetworks?api-version=2020-08-01 HTTP/1.1" 200 133
DEBUG: azure.core.pipeline.policies._universal: Response status: 200
DEBUG: azure.core.pipeline.policies._universal: Response headers:
DEBUG: azure.core.pipeline.policies._universal: 'Cache-Control': 'no-cache'
DEBUG: azure.core.pipeline.policies._universal: 'Pragma': 'no-cache'
DEBUG: azure.core.pipeline.policies._universal: 'Content-Type': 'application/json; charset=utf-8'
DEBUG: azure.core.pipeline.policies._universal: 'Content-Encoding': 'gzip'
DEBUG: azure.core.pipeline.policies._universal: 'Expires': '-1'
DEBUG: azure.core.pipeline.policies._universal: 'Vary': 'Accept-Encoding'
DEBUG: azure.core.pipeline.policies._universal: 'x-ms-ratelimit-remaining-subscription-reads': '11996'
DEBUG: azure.core.pipeline.policies._universal: 'x-ms-request-id': '7ca9ef1a-8215-484d-b1f4-921ed6f727ab'
DEBUG: azure.core.pipeline.policies._universal: 'x-ms-correlation-request-id': '7ca9ef1a-8215-484d-b1f4-921ed6f727ab'
DEBUG: azure.core.pipeline.policies._universal: 'x-ms-routing-request-id': 'NORTHEUROPE:20210312T085031Z:7ca9ef1a-8215-484d-b1f4-921ed6f727ab'
DEBUG: azure.core.pipeline.policies._universal: 'Strict-Transport-Security': 'max-age=31536000; includeSubDomains'
DEBUG: azure.core.pipeline.policies._universal: 'X-Content-Type-Options': 'nosniff'
DEBUG: azure.core.pipeline.policies._universal: 'Date': 'Fri, 12 Mar 2021 08:50:30 GMT'
DEBUG: azure.core.pipeline.policies._universal: 'Content-Length': '133'
DEBUG: azure.core.pipeline.policies._universal: Response content:
DEBUG: azure.core.pipeline.policies._universal: {"value":[]}
(...)
```

Output from Cloud Shell in Azure Portal:
```
(...)
DEBUG: azure.core.pipeline.policies._universal: Request URL: 'https://management.azure.com/subscriptions/ec0308fb-8d6e-497a-9dd6-99c7d9ab7962/resourceGroups/unicorn-dev-euw-aksresources-rg/providers/Microsoft.Network/virtualNetworks?api-version=2020-08-01'
DEBUG: azure.core.pipeline.policies._universal: Request method: 'GET'
DEBUG: azure.core.pipeline.policies._universal: Request headers:
DEBUG: azure.core.pipeline.policies._universal: 'Accept': 'application/json'
DEBUG: azure.core.pipeline.policies._universal: 'x-ms-client-request-id': '1aa7c576-830f-11eb-a13f-0a580af4c047'
DEBUG: azure.core.pipeline.policies._universal: 'CommandName': 'network vnet list'
DEBUG: azure.core.pipeline.policies._universal: 'ParameterSetName': '-g --debug'
DEBUG: azure.core.pipeline.policies._universal: 'User-Agent': 'AZURECLI/2.20.0 (DEB) azsdk-python-azure-mgmt-network/17.1.0 Python/3.6.10 (Linux-4.15.0-1108-azure-x86_64-with-debian-10.2) cloud-shell/1.0'
DEBUG: azure.core.pipeline.policies._universal: 'Authorization': '*****'
DEBUG: azure.core.pipeline.policies._universal: Request body:
DEBUG: azure.core.pipeline.policies._universal: This request has no body
DEBUG: urllib3.connectionpool: Starting new HTTPS connection (1): management.azure.com:443
DEBUG: urllib3.connectionpool: https://management.azure.com:443 "GET /subscriptions/ec0308fb-8d6e-497a-9dd6-99c7d9ab7962/resourceGroups/unicorn-dev-euw-aksresources-rg/providers/Microsoft.Network/virtualNetworks?api-version=2020-08-01 HTTP/1.1" 200 None
DEBUG: azure.core.pipeline.policies._universal: Response status: 200
DEBUG: azure.core.pipeline.policies._universal: Response headers:
DEBUG: azure.core.pipeline.policies._universal: 'Cache-Control': 'no-cache'
DEBUG: azure.core.pipeline.policies._universal: 'Pragma': 'no-cache'
DEBUG: azure.core.pipeline.policies._universal: 'Transfer-Encoding': 'chunked'
DEBUG: azure.core.pipeline.policies._universal: 'Content-Type': 'application/json; charset=utf-8'
DEBUG: azure.core.pipeline.policies._universal: 'Content-Encoding': 'gzip'
DEBUG: azure.core.pipeline.policies._universal: 'Expires': '-1'
DEBUG: azure.core.pipeline.policies._universal: 'Vary': 'Accept-Encoding'
DEBUG: azure.core.pipeline.policies._universal: 'x-ms-request-id': '71fbdd59-3b3f-480a-b1f8-564014cff345'
DEBUG: azure.core.pipeline.policies._universal: 'x-ms-correlation-request-id': '14089693-8490-4d0a-a745-cc2519a00482'
DEBUG: azure.core.pipeline.policies._universal: 'x-ms-arm-service-request-id': '1d77dda7-70fb-4b68-a097-8b6736131fc1'
DEBUG: azure.core.pipeline.policies._universal: 'Strict-Transport-Security': 'max-age=31536000; includeSubDomains'
DEBUG: azure.core.pipeline.policies._universal: 'Server': 'Microsoft-HTTPAPI/2.0, Microsoft-HTTPAPI/2.0'
DEBUG: azure.core.pipeline.policies._universal: 'x-ms-ratelimit-remaining-subscription-reads': '11996'
DEBUG: azure.core.pipeline.policies._universal: 'x-ms-routing-request-id': 'WESTEUROPE:20210312T084406Z:14089693-8490-4d0a-a745-cc2519a00482'
DEBUG: azure.core.pipeline.policies._universal: 'X-Content-Type-Options': 'nosniff'
DEBUG: azure.core.pipeline.policies._universal: 'Date': 'Fri, 12 Mar 2021 08:44:06 GMT'
DEBUG: azure.core.pipeline.policies._universal: Response content:
DEBUG: azure.core.pipeline.policies._universal: {
"value": [
{
"name": "aks-vnet-85333569",
"id": "/subscriptions/ec0308fb-8d6e-497a-9dd6-99c7d9ab7962/resourceGroups/unicorn-dev-euw-aksresources-rg/providers/Microsoft.Network/virtualNetworks/aks-vnet-85333569",
"...": "... long JSON content here"
}
]
(...)
```

Full output of `az cli --debug` is attached:
[2021-03-12_08-35-24-run-from-azure-pipelines-returns-empty-array.txt](https://github.com/Azure/azure-cli/files/6129714/2021-03-12_08-35-24-run-from-azure-pipelines-returns-empty-array.txt)
[2021-03-12_08-44-06-run-from-azure-portal-cli-returns-correct-result.txt](https://github.com/Azure/azure-cli/files/6129715/2021-03-12_08-44-06-run-from-azure-portal-cli-returns-correct-result.txt)
[2021-03-12_08-50-30-run-from-azure-pipelines-returns-empty-array-again.txt](https://github.com/Azure/azure-cli/files/6129716/2021-03-12_08-50-30-run-from-azure-pipelines-returns-empty-array-again.txt)