You perform an agentless backup of a Hyper-V virtual machines using Agent for Hyper-V on Windows Server 2016 or higher.
After you run the backup task, virtual machines show unexpected behavior, e.g. VM temporarily freezes or automatic failover to a replica happens (when failover is automated by 3rd party software).
Acronis uses native Microsoft Hyper-V API (WMI) to trigger creation of a VM production checkpoint, which may lead to unexpected VM behavior due to temporary disk I/O freezes inside the guest OS which may occur during checkpoint creation. The process of production checkpoint creation is fully performed on Hyper-V level and is not controlled by Acronis. After the VM production checkpoint is created by Hyper-V, Acronis Agent for Hyper-V opens disks from the snapshot as block devices to read data from them using "Win32 API" method as one of the recommended by Microsoft - see details at Hyper-V Backup Approaches.
If certain software on virtual machines is sensitive to disk I/O freeze, running agentless backup may therefore cause unexpected behavior on such VMs.
To check whether the issue is caused by Acronis Backup, try to create a VM production checkpoint directly via Hyper-V Manager without using Acronis Backup:
1) In Hyper-V manager right click on any VM where the issue reproduces, then go to Management -> Checkpoints, and select Enable Checkpoints, then Production Checkpoints and deselect the checkbox Create standard checkpoints if it's not possible to create production checkpoint.
2) After specifying these options, try to create a checkpoint of this virtual machine via Hyper-V Manager and check if the issue reproduces.
If the freeze or other unexpected behavior such as failover happens during production checkpoint created as described above, the issue is caused by the specifics of virtual machine configuration. If adjusting configuration to avoid errors during agentless backup is not possible, as a workaround, you can install Agent for Windows / Agent for Linux inside the virtual machine and perform agent-based backup.
If checkpoint is created correctly but making an agentess backup still causes unexpected behavior, collect system information from the affected server and contact Acronis Customer Central with a reference to this article
When backing up virtual machines on Windows Hyper-V Server 2012, keep in mind the following specifics:
1) The entire volume where the VM resides will be snapshotted.
2) Backup of even a single VM in Windows Hyper-V Server 2012 will take snapshot of the entire volume and this is an expected behavior for this operating system.