Thanks Alexandre. I have found the issue, the unit is working on Wifi and won't connect via Ethernet. I have tried different cables which are definitely not broken. I am going to swap units and check...

Hi, I have just set up Deco S4 three units. The main unit is in the front room, the second unit is wired and at the back of the house connect via 30m long cable. The third unit is on the first floor...