Hyper-V error when enabling replication

I am trying to enable replication between two servers running Windows 2012 in different data centers. I've configured them for certificate validation over https. When I attempt to enable replication from the source server, when I click Finish it fails with this:

[Window Title]
Enable Replication

[Main Instruction]
Enabling replication failed.

[Content]
Hyper-V failed to enable replication.

[Expanded Information]
Hyper-V failed to enable replication for virtual machine 'MYTESTVM': A virtual disk support provider for the specified file was not found. (0xC03A0014). (Virtual machine ID blah..blah)

In the "Choose Replication VHDs" I see (and have checked) the two disk images, ex. C:\VM\MYTESTVM_12345-aaaa-bbbb-cccc-123456.avhdx

These machines are not part of a failover cluster or a domain.

Any chance you have:

• An "interesting" backup solution on the hosts?
• Have pre-existing checkpoints, or external disks such as iSCSI, virtual fibre channel, or shared VHDX?