To enable extended logging of SPNs used during connections, create the following registry value on the Veeam Backup Server and all servers listed under Backup Infrastructure > Microsoft Windows.
Key Location: HKLM\SOFTWARE\Veeam\Veeam Backup and Replication\
Value Name: KerberosExtendedLogging
Value Type: DWORD (32-Bit) Value
Value Data: 1
PowerShell cmdlet to Enable KerberosExtendedLogging