I've updated my router from TP-Link Archer C3150 to TP-Link Archer AX1800 (AX20). 

My ISP is Virgin Media and I have their latest Superhub 4 router. My previous configuration (the one I was trying to keep) was:
 

Virgin Media in modem mode -> Archer C3150 (dynamic IP 86.6.x.x) -> Lan+Wifi 192.168.1.x

However, when I connected new router AX1800 it was unable to get dynamic IP from modem. 

Configurations that do work are:

Virgin Media in modem mode -> Archer C3150 (dynamic IP 86.6.x.x) -> Lan+Wifi 192.168.1.x -> cable to AX1800 (dynamic IP 192.168.1.100) -> Lan + Wifi 192.168.2.x

Virgin Media in router mode -> AX1800 (dynamic IP 192.168.0.x) -> Lan + Wifi 192.168.1.x

But there is no way to setup it in modem mode. 

Virgin Media in modem mode -> AX1800 (dynamic IP 86.6.x.x) -> Lan+Wifi 192.168.1.x - the "internet" LED stays orange, and no IP is assigned to WAN interface. All standard magic like restarting modem, router, replacing cable , ... completed. 

Could it be some issue in AX1800's dhcp client that it doesn't allow external (non 192.168.x.x) IP address? I had no such issue with previous router. 

Any help appreciated.

Kind regards,

Andrzej