Agentless backup of Hyper-V VMs with pass-through disks finishes with a warning:
Cannot take checkpoint for 'MachineName' because one or more pass-through disks are attached.
Agent for Hyper-V does not back up pass-through disks. During backup, the agent skips these disks and adds warnings to the log.
You can avoid the warnings by excluding pass-through disks from the protection plan.
If you want to back up pass-through disks or data on these disks, install an agent in the guest operating system.