OpenVPN Routing

[teknoadmin]

Ok, last post was silly, I have to admit.
I will try again simplifying a bit.

Networks :

(A) LAN 172.16.10.0/24, OpenVPN Client GW 10.20.51.2/30 (ovpnc1)

(B -> A) OpenVPN Server GW 10.20.51.1/30 (ovpns1)
(B -> C) OpenVPN Server GW 10.20.53.1/30 (ovpns2)

(C) LAN 172.18.10.0/24, OpenVPN Client GW 10.20.53.2/30 (ovpnc1)

Goal : multi hop OpenVPN with policy based routing. I don't want to use static routes.

If I ping, for example, from (C) 172.18.10.10 to (A) 172.16.10.10, ICMP request arrive correctly to (A) host, but reply don't route back correctly, it exits to WAN interface of (B).

On (B), I see ICMP reply on ovpns1, and on that interface there's the following rule :

Protocol : IPv4*
Source : 172.16.10.0/24
Port : *
Destination : 172.18.10.0/24
Port : *
Gateway : ovpns2 gateway (10.20.53.2)

Anyway, traffic exits from WAN.
The same happens in the opposite way from (A) to (C).

If I add a static route on (B) with :

Network : 172.18.10.0/24
Gateway : ovpns2 gateway (10.20.53.2)

Suddenly traffic is routed correctly back.

What am I missing here?
Do you have any suggestion?

Thank you