Scheduled backup does not work but can be taken manually.
There are hanged
pmm-ras and backup process(es) on the management node.
The service nodes where the backup operation was being executed was restarted.
Backup manager did not throw an error but looped itself indefinitely waiting for the
/usr/local/psa/admin/bin/pmmcli --get-task-status to return status
The behavior in known as software issue PPA-2347.
In case the udpate cannot be installed right away the workaround for the issue is to kill the hanged
pmm-ras and backup processes on the management node.