Backups using a specific hardware provider do not work, provider is missing from the user interface:
Veeam fails over to a software provider which does not have the functionality of a hardware provider (e.g. off-host proxy, fast snapshot creation, etc.)
On the Veeam Backup & Replication server, please create the following registry key:
HKLM\SOFTWARE\VeeaM\Veeam Backup and Replication UIShowAllVssProvidersForVolume
After creating the registry key, please restart the Veeam services and make sure that the required provider is visible and can be selected.