Spec net configuration with two router with middle server and openvpn

I'm working on something. i'm created two openwrt router with a middle server with this config below.

The goal is:

The road warrior router connect to middle server, the static router connect too to middle server, and the roadwarrior router's one interface, "bridged" in the static router's lan interface (of course this config has 3 bridge but the goal is looks like one). and the machine on the roadwarrior router looks like in the static's router lan.

the middle server is necessary because the two router is on an LTE network, behind the provider's NAT. (no public ips)

All things working good except the dhcp not gave default gateway. Or the client not accept it. got an IP address, netmask but no gateway. If i put in manually the default route the system is working.

Have anybody an idea why no not got a gateway?