[Premium] Redeploying Azure Function integrated with VNET fails

**Describe the bug**
We are using newly Azure Function with VNET integration and to automate deployments and integration, we followed this [tutorial](https://github.com/Azure/Azure-Functions/issues/1284).
It works for first deployment ,but then if you try to redeploy for any change, it fails with unclear error.
`"status": {
"value": "Failed",
"localizedValue": "Failed"
},
"subStatus": {
"value": "BadRequest",
"localizedValue": "Bad Request (HTTP Status Code: 400)"
},
"submissionTimestamp": "2019-11-14T14:19:59.1587288Z",
"subscriptionId": "************************",
"properties": {
"statusCode": "BadRequest",
"serviceRequestId": null,
"statusMessage": "{\"error\":{\"code\":\"InternalServerError\",\"message\":\"There was an unexpected InternalServerError. Please try again later. x-ms-correlation-request-id: ****************"}}"
}`

**To Reproduce**
Steps to reproduce the behavior:
1. Create an arm template that deploys an Azure function with all resources, follow [this](https://github.com/ScottHolden/ARMExamples/blob/master/AppService-VnetNew-Storage/deploy.json).
2. Deploy your template through some pipelines.
3. It works.
4. Try to redeploy, you get an internal error.

**Expected behavior**
Function gets deployed normally in both incremental or complete mode.