We installed three X20s yesterday as per instructions in the app. One X20 is attached to a Virgin Media Hub 3 which is running in modem mode, and the other two have been connected to the first via a Netgear GS724T Ethernet switch.

This evening, the two satellite Decos have disconnected from Ethernet backhaul, even though according to the switch there is an active link to each of them. Having power-cycled everything and checked the integrity of the wiring, I cannot persuade them to reconnect. Oddly, the switch reports the satellite Decos being connected at 100 Mbps rather than 1000 as they were yesterday, though the main Deco is connected at 1000 Mbps. 

All Decos performed firmware updates yesterday. 
 

Any suggestions, please?