++ VM on second Hyper-V Cluster Node not backing up - Failed to find VM ++

Hello,
we are using NetVault 12.1 to backup all virtual machines from our hyper-v 2012R2 cluster.
vms01 (node1) vms01 (node2) vmscl (cluster). Ping, nslookup/ptr, check access, firewall test is running successfully.

For some weeks we see the following messages in the backup log.

Job Message    2018/10/29     18:00:02  71        Data Plugin       VMS01 Number of VMs selected for backup: 20

Error         2018/10/29     18:00:05          71        Data Plugin       VMS01 VM [BI01]: Failed to find VM on cluster 'VMSCL'
Error         2018/10/29     18:00:06          71        Data Plugin       VMS01 VM [BI01]: Backup failed
Error         2018/10/29     18:00:10          71        Data Plugin       VMS01 VM [CLOUD]: Failed to find VM on cluster 'VMSCL'
Error         2018/10/29     18:00:10          71        Data Plugin       VMS01 VM [CLOUD]: Backup failed

Here is what I did to get it running again:
- Removed all agents on vms02, restart
- Deleted virutal client
- Created new virtual client with the cluster name "vmscl" (agents are installed on vms02 successfully)
- Restarted
- Hyper-V Cluster license is looking good
- Running the following commands

Import-Module FailoverClusters
Import-Module ServerManager

Remove-ClusterNode -Cluster vmscl vms02
Restarted vms02
Add-ClusterNode -Cluster vmscl vms02

Get-ClusterNode -Cluster vmscl
Name            ID    State
----                 --    -----
VMS01          2     Up
VMS02          1     Up

Virtual machines running on vms02 are still not backing up / shown in the create backup selection section.