Unable to change virtual disk settings for a VM after restore if the VM had user checkpoints during a backup that used the WMI method
If a virtual machine has any user-created checkpoints when a NetBackup WMI backup starts, NetBackup includes the checkpoint .avhdx files in the backup image. When the VM is restored from that backup, the .avhdx files are not automatically merged back to the VM's parent disks. As a result, certain settings for the restored VM cannot be changed (such as the virtual hard disk). The Hyper-V Manager states: "Edit is not available because checkpoints exist for this virtual machine."
This problem is due to a Microsoft issue. As a workaround, manually create and delete a user checkpoint for the restored VM. This action triggers an automatic disk merge for all the .avhdx files. After the merge, the VM settings can be changed.