Create Operation Intermittently failed while creating multiple Network Watcher Flow Logs with Network Security Group in parallel

We are aware of that [Create operation](https://github.com/Azure/azure-rest-api-specs/blob/main/specification/network/resource-manager/Microsoft.Network/stable/2021-05-01/networkWatcher.json#L2040) Intermittently failed and threw below error message while creating multiple Network Watcher Flow Logs with Network Security Group in parallel. Some times unable to create NSG flow logs, some times not. Seems API is unstable. We expect all Network Watcher Flow Logs with NSG should be created successfully. Could you help take a look and fix the issue? Thanks in advance.

Error Message:
```
Code="InternalServerError" Message="An error occurred." Details=[]
```

Start with specification/network/resource-manager/Microsoft.Network/stable/2021-05-01/networkWatcher.json at the Create operation linked in the issue. Reproduce parallel Network Watcher Flow Log creation with Network Security Groups and determine whether the REST specification can address the intermittent InternalServerError; done requires a confirmed fix or a documented service-side finding.

Written by the indexing model from the issue text.