Clustered openVPN with DCO fails

[rac-hh]

I configured a new openVPN instance with DCO on a 24.7.9_1 test system. After all tests I configured the same vpn instance on our productive 24.10.1 cluster. Client can connect, but there is no data traffic and the client reconnect after ping-restart timeout.

Further tests:
* Switching to TUN on client/server works
* changeing the server IP in the client config to the WAN IP of the active node works (with DCO)
* changeing the server IP in the client config to the Cluster IP of the active node fails as described above (with DCO)

I see ACK network pakets from the servers the client tries to connect in the opnSense firewall, but it seems they don't leave the server through the data tunnel.

Has someone a working DCO configuration in a Cluster?
Some other hints?