OpenVPN client slower on wired interface

Hi all, excuse me if this is already discussed somewhere on the forum.

Using openvpn client on Turris Omnia without problems for several months. All this time it was used through a separate WLAN and was maxing the available bandwidth from the server (~30Mbits). Rough description of the setup:

          WAN (eth1) -> LAN1 (eth0, wlan0)

mwan3

         OVPN (tun0) -> LAN2 (wlan1)

Just recently I needed to use the VPN on one of the wired ports on the router. eth2 was bridged.

        OVPN (tun0) -> LAN2 (wlan1, eth2)

The setup worked, but to my surprise, when using the VPN through the wired port (eth2, port lan4) maximum speed achieved was ~7Mbit (compared to 30 Mbit via wlan). I tried also using eth0 and any of the other LAN ports, with same result.

Any help what might cause this is very welcome. For me most puzzling is why it works fine through wireless, but is slower via cable.

Thanks in advance.