get-vm shows integration services version as 0.0

We're running Hyper-V 2016, and have upgraded the VM version of most machines to 8.0, but still have some at 5.0.  There's a mix of generation 1 & generation 2 VMs.

Now, when we run:

get-vm | ft Name, IntegrationServicesVersion

it returns the Integration Services Version as 0.0 for ALL VMs, including the Linux VMs.

In Failover Cluster manager, the Integration Services versions are correct.

A search only returns a single other incident like this, and the fix then was to apply a hotfix that has since been expired/removed.