In Hyper-V 2016 Microsoft implemented a possibility to share a virtual hard disk (in .vhdx or .vhds format only) between two or more VMs and use that virtual hard disk as a shared storage when building guest clusters.
When you decide to add a Windows Server 2016 Hyper-V cluster to Veeam console, you must decide where to store meta files created during the backup process of the VMs from the shared virtual hard disk (i.e. information about snapshot groups etc.).
By default, meta files location is not defined, so you need to define it manually.