Inconsistent Output to az vm update with --what-if

[Toluwaloope]

Issue Type

Bug Report

Description

I created a virtual machine with the command below

az vm create -n '<vm-name>' -g '<resource-group>' --image Win2022Datacenter --size 'Standard_B2ms' --vnet-name '<vnet-name>' --subnet '<subnet-name>'

I decided to upsize the server to Standard_B4ms and noticed an inconsistency in the --what-if output when I executed the command 4 times in a row.

Command or Script

az vm update --resource-group '<rg-name>' --name '<vm-name>' --set hardwareProfile.vmSize=Standard_B4ms --what-if

Expected Behavior

Resource and property changes are indicated with this symbol:
  ~ Modify

The deployment will update the following scope:

Scope: /subscriptions/<subscriptionid>/resourceGroups/<resource-group-name>

  ~ Microsoft.Compute/virtualMachines/<vm-name> [2025-04-01]
    ~ properties.hardwareProfile.vmSize: "Standard_B2ms" => "Standard_B4ms"

Resource changes: 1 to modify.

Actual Behavior

Resource and property changes are indicated with this symbol:
  ~ Modify

The deployment will update the following scope:

Scope: /subscriptions/<subscriptionid>/resourceGroups/<resource-group-name>

  ~ Microsoft.Compute/virtualMachines/<vm-name> [2025-04-01]
    ~ properties.hardwareProfile.vmSize:                  "Standard_B2ms" => "Standard_B4ms"
    ~ properties.networkProfile.networkInterfaces: [
      ~ 0:

        ~ id: "/subscriptions/<subscriptionid>/resourceGroups/<resource-group-name>/Microsoft.Network/networkInterfaces/<nic-name>" => "/subscriptions/<subscriptionid>/resourceGroups/<resource-group-name>/providers/Microsoft.Network/networkInterfaces/defaultValue"

      ]
    ~ properties.osProfile.adminUsername:                 "<admin-username>" => "defaultValue"
    ~ properties.storageProfile.imageReference.offer:     "WindowsServer" => "UbuntuServer"
    ~ properties.storageProfile.imageReference.publisher: "MicrosoftWindowsServer" => "Canonical"
    ~ properties.storageProfile.imageReference.sku:       "2022-datacenter-g2" => "18.04-LTS"
    ~ properties.storageProfile.osDisk.name:              "test-whatif-vm_OsDisk_1_db22fbcb060944d6953000750b63c40e" => "osdisk"

Resource changes: 1 to modify.

Environment

• OS: macOS Tahoe 26.1
• Tool Version: Azure CLI 2.81.0.post20251202050623
• Python Version: 3.12.10

Additional Context

No response

[yonzhan]

Thank you for opening this issue, we will look into it.