@David-TP hi, and sorry for slow response. Switch is a Netgear GS208 gigabit switch. I have tried multiple switches and even just the BT Home Hub with Decos, same problem happens so I exclude the...

My setup looks like this: BT Broadband Hub - wifi disabled, hard wired into a switch Deco X75 mesh (3 units) - hard wired to same switch as router Sky Q 2Tb - hard wired to switch (note, both wifi...