New xb8-t: LAN ports disabled in bridge mode?

Hey there - have a brand new xb8-t and am attempting to use an Asus BT10 mesh router. 

When I place the xb8-t in bridge mode, no LAN ports provide internet. I have confirmed with via the router connection and also by connecting a PC to the modem directly via Ethernet.  If I understand correctly one port should remain active in bridge mode.  Have performed a full factory reset of both the modem and router twice. Firmware it up-to-date. Current setup: I've just disabled all wi-fi radios on the xb8-t.

When the vb8-t is not in bridge mode, all ports provide internet and the ASUS is OK - though I do encounter occasional DHCP errors. 

Any ideas?