VMware backup job fails with "Exception of type 'Veeam.Backup.AgentProvider.AgentClosedException' was thrown"

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.

More Information

https://kb.vmware.com/s/article/2125497