Symmetric NAT conflict with port forwarding

Question

I have one server behind NAT router that already set up port forwarding to server port 7000(server-client talk UDP). Everything is fine, except sometime the packet that is sent to client is not from port 7000, so firewall on client side drop it.

Symmetric NAT map out-going source port to another port, when this server connect with more than one client.

I already setup port forward and think that NAT won't overwrite my rule.

Anyone has an idea ?

thanks in advance ^^ voteforpedro