Bit of a stupid problem, I am sure I have just failed to set something up properly.....
Under normal conditions the modem and router (er-x). followed the guide (
https://kitz.co.uk/routers/zyxel_VMG8324-B10A_bridge.htm) inc section 5 and
https://forum.kitz.co.uk/index.php?topic=20901.0My interface groups are set as "default" LAN 2 - 4 and "Bridge" LAN1
My default interface has the address 192.168.0.100 and Bridge has 192.168.2.1 (both have 255.255.255 netmasks)
The LAN Information MAC address is reserved in the ER-x as the 192.168.0.100 address
All works normally and I can get diagnostics using dslstats ok.
However, if I reboot the router, sometimes it does not reconnect to the WAN but I think gets served a DHCP address served from itself (via the diagnostics connection). It will then ultimately go into a boot cycle.
If I pull the diagnostics connection out of the modem, the router will boot up as expected.