Altaro backup warning

I have a VM, which was originally running on Windows Server 2008 R2 with the Hyper-V role. The guest was a Server 2012 which was just serving as a domain controller (a backup one to the SBS 2011 server running on another physical machine).

I moved the VM by shutting it down, copying the files to a new Hyper-V Server 2016 host, and used Hyper V manage to Import the VM. The Altaro backup succeeds but with a warning "Backup snapshot is not application consistent. Backup will proceed in crash-consistent mode."

On the VM's event logs, I have these messages:

ESENT: lsass (592) An attempt to open the file "\\?\Volume{b0cbe895-ed69-11e6-80b0-806e6f6e6963}\Windows\NTDS\ntds.dit" for read only access failed with system error 32 (0x00000020): "The process cannot access the file because it is being used by another process. ". The open file operation will fail with error -1032 (0xfffffbf8).

VSS: A VSS writer has rejected an event with error 0x800423f4, The writer experienced a non-transient error. If the backup process is retried, the error is likely to reoccur. . Changes that the writer made to the writer components while handling the event will not be available to the requester. Check the event log for related events from the application hosting the VSS writer.

vmicvss: The VSS writer NTDS failed with status 11 and writer specific failure code 0x800423F4.

I thought it was a problem with the move from a 2008 R2 host to 2016, so I demoted the domain controller, removed the AD & DNS roles, and then did a clean install of Server 2012 R2, re-added the roles and promoted the server back to a DC, but the problem persists.

Any ideas? It seems like something on the VM is causing the snapshot to fail, but I'm not sure how I'd fix a file access issue for something related to the directory service.

Apparently this is a known issue with Hyper-V 2016 AND 2012 R2 domain controllers as a VM. Microsoft should be working on a fix for that.