Challenge
After upgrade to Veeam 9.5 Update 4, VMware backup jobs might fail with the error "Exception of type 'Veeam.Backup.AgentProvider.AgentClosedException' was thrown" while backing up virtual machines from vSphere 6.0 if a backup proxy has IPv6 enabled on one or more network interfaces.
Cause
It is a known issue affecting VMware Virtual Disk Development Kit (VDDK) 6.0.
Solution
Disable IPv6 on the network interfaces of the backup proxy.