[BUG] GET MICROSOFT.INSIGHTS/DIAGNOSTICSETTINGS return 404 after a successful PUT

### API Spec link

https://github.com/Azure/azure-rest-api-specs/blob/48dcf5d28914f6d5ba2d66aa1689241b29bac49d/specification/monitor/resource-manager/Microsoft.Insights/preview/2021-05-01-preview/diagnosticsSettings_API.json#L80-L85

### API Spec version

2021-05-01-preview

### Describe the bug

PUT/SUBSCRIPTIONS/RESOURCEGROUPS/PROVIDERS/MICROSOFT.COMMUNICATION/COMMUNICATIONSERVICES/PROVIDERS/MICROSOFT.INSIGHTS/DIAGNOSTICSETTINGS/ returns 200 but GET/SUBSCRIPTIONS/RESOURCEGROUPS/PROVIDERS/MICROSOFT.COMMUNICATION/COMMUNICATIONSERVICES/PROVIDERS/MICROSOFT.INSIGHTS/DIAGNOSTICSETTINGS/ return 404

### Expected behavior

GET after successful PUT should not return 404

### Actual behavior

GET after successful PUT return 404

### Reproduction Steps

cannot be stably reproduced, but a case was recorded with correlationId=='9f63fb96-4cc3-d05b-9b73-a09552840473'
resource URL: https://management.azure.com/subscriptions/XXXX/resourceGroups/s00803Nrgpslcm1933-dev/providers/Microsoft.Communication/communicationServices/s00803Nacs009999slcm1933dev/providers/Microsoft.Insights/diagnosticSettings/s00803Nacs009999slcm1933dev-securitylogs?api-version=2021-05-01-preview

where at 2024-08-15T19:36:24.2711282Z the PUT return 200 but at 2024-08-15T19:36:24.5175452Z the GET return 404.

### Environment

Terraform Azurerm provider https://github.com/hashicorp/terraform-provider-azurerm/issues/27087

Start with specification/monitor/resource-manager/Microsoft.Insights/preview/2021-05-01-preview/diagnosticsSettings_API.json at lines 80-85 and compare the documented PUT and GET operations. Use the recorded resource URL and correlation ID, together with the linked Terraform issue, to establish whether the specification or service behavior is responsible; done means a confirmed diagnosis and a clearly scoped specification change or follow-up.

Written by the indexing model from the issue text.