Backing up a Windows Server 2016 machine with Hyper-V VMs running on it results in base images of the volumes the VM VHD & VHDX files reside on. For example, if the VHD or VHDX files for a running VM are on D:, the D: volume will continuously base image while a running VM is on it.
In the Agent System Events you will find Event ID 9267 AAVolFlt:
Unexpected base images for D:
Event ID 9267
Log write failed for device \Device\HarddiskVolume5 (drive D:). The failure status code is the last word of the data.