Gateway, VLAN config etc. is fine. Everything works from the LAN/VLANs as intended. The only issue I have is that the port forward does not work. It actually does work in the sense that requests are forwarded to the server but the reply of the server is not travelling back through the Firewall. So the client just times out. If a client from LAN connects to the server in VLANx it works perfectly fine. But then this is simple routing and not DNAT.