Please ensure that you are running Macrium Reflect v6.1.1309 or later.
Disk images cannot be used to backup Hyper-V Cluster Shared Volumes.
Server 2012R2 Hyper-V Cluster Shared Volumes (CSV) can be backed up using the File and Folder backup functionality in Macrium Reflect. Earlier versions of Windows are not supported.
You must use the File and Folder restore functionality to restore VHD and VHDX files. You cannot mount/browse backup files and use Copy and Paste to restore files larger than 4GB