I found a solution:
xe template-param-set uuid=8d8bcde8-ebbd-1d0c-7086-58a08602cf02 is-a-template=false
But that shouldn't be necessary... XOA build 20200228 XCP-ng 8.1.0

Hi, I just tried the following sequence attempting to get a clean offline backup of a VM:

• shutdown the VM
• took a snapshot
• restarted the VM
• "create a VM from this snapshot" in XOA
  The result is that I can see the expected additional 100GB virtual disk on the host under Storage-Local Storage-Disks. But no new VM appeared on the host (or any other host) whether in XOA, xcp-ng center, or the CLI.

 xe vdi-list params=all (using the uuid from XOA) shows the disk, with one vbd-uuid. Using that:
 xe vbd-list uuid=28d567fa-73ed-d945-0f00-b14856340395
uuid ( RO)             : 28d567fa-73ed-d945-0f00-b14856340395
          vm-uuid ( RO): 8d8bcde8-ebbd-1d0c-7086-58a08602cf02
    vm-name-label ( RO): cem01vs4-cold-20200501-vm
         vdi-uuid ( RO): 0a3281e0-e709-4d68-93a5-562ea0720924
            empty ( RO): false
           device ( RO): xvda

vm-name-label is indeed the name I gave the vm when creating it from the snapshot.
and with params=all the only thing that looks odd is "allowed operations (SRO) :" (blank)

However: xe vm-list knows no such VM, and xe vm-export can't find it by UUID or by name.
The whole objective of the exercise is to export the newly-created VM to offline storage (preferably compressed)...

Any ideas what happened or how to fix it?