Veeam error after Hyper-V migration

In general I find Veeam backup and replication 9 performs brilliantly once it's configured.  But sometimes infrastructure changes can really throw it for a loop.  I recently had to shuffle several VMs around between Hyper-V hosts using the built-in Move command and afterwards Veeam started throwing errors on some of the VMs. (Task failed:  failed to expand object.  Error:  Cannot find VM on host...)

The main thing they all had in common was they they were configured to use alternate guest OS credentials (which Veeam uses to take the internal snapshots).  In the Veeam GUI these all appear to be tagged by VM Name but what I suspect is that on the back end it's latched on either to the GUID or the host server name so by Moving the VMs it started treating them as new entities.

The fix is a relatively straightforward but manual process of removing them, adding them back from the new associated servers (under Guest Processing, Credentials...), setting the right credentials for them, then hitting OK, then Finish.  That will fix that particular error so you won't see it again on the next run.