"save ..." command doesn't reach the client

Backup (file level) on one of the nodes in a SQL cluster is not running.

Networker Server V9.1.1.3.Build.189

Windows Server 2012 Std.
NW client --> 9.1.1.9.Build.394 (also tested 9.1.1.7)

############## another environment with the same issue #############
Windows Server 2016 Std.
NW client --> 9.1.1.9.Build.394
####################################################################

A try to backup C:\ ends in a time out of pseudo saveset (30 min).
There are no Problems on another MS SQL HAG node, same config.

The backup was runnning before. The communication (IP, port, firewall ect.) is given, checked with tcpdump many times.
DNS is correct for server, client, storage node and data domain. Also checked, many times between the components.

The NIC on both nodes in the cluster has multiple IPv4 addresses.

Already reinstalled the client (incl. deleting ...\EMC NEtworker\) and updated the NSR Peer Information.
The server entry in the servers file is set.

There are no log entries regarding errors or warnings on the server, even in the daemon.raw on the client.
Only with the command "dbgcommand -p PID D=9" on the client I can see more in the daemon.raw, but no errors as well.

Networker checks the backup by savefs (successully) and that's all. The real "save ..." command doesn't raech the client.

I can start the backup from the client by the "NetWorker User", it's running.
Also, I can start the backup by copying the "save ..." command from NMC action log.
In both cases the backup is running successfully.

I've checked everything … no ideas anymore