openVPN with DCO fails after Upgrade

[rac-hh]

I had a working DCO instance. After Upgrade 24.7.12 -> 25.1 the connection is established, but no traffic. Regular reconnects due to keepalive parameter.

Even pings to the serverside IP of the tunnel get no answers. Similar to Ticket #8178, but without clustering.

Client is openVPN 2.6.13 on windows (which worked with opnSense 24.7.12).