Thanks for the suggestion but in the end I already did a factory reset which put it back in router mode & disabled the Wi-Fi manually.
Modem mode seems to behave strangely with regards to the Ethernet ports.
I excepted only one per to bridge the internet connection but it seems all of them do at the same time.
In the end, the connect box as a non-WiFi router and two Wi-Fi access points on subdomains seems to work fine for me anyway.
Gabbo