I have an old MR400, 4 ethernet ports, sharing Internet connection from my Android phone through Ethernet (usbc adapter) perfectly fine.

Only concern being  MR400 has 100Mbps ethernet port while my Mobile access (being 5G) is 3-4x times faster.

I decided to upgrade for an Archer C6 but cant make it work.

Description of my setup:

Mobile phone                                                                        Archer C6                                                  Wired devices

192.168.20.70                 ---------- Ethernet ---------- WAN port | LAN Ports -------Ethernet---- DHCP 192.168.0.100-250

(2 last bytes are random)                                   192.168.20.0/24 | 192.168.0.1/24

Everything should work fine but when I start the archer C6 he has connection (Wired devices have connection too) but after a very short time (30-60sec max)

internet connection is lost (led turns from green to orange).

From the wired device I could only ping the router 192.168.0.1 but nothing else

It looks like a routing issue but there is no way to configure that. I don't really know what to do. I tried playing with settings disabling NAT/Firewall... but nothing worked.