@David-TP thank your for your prompt reply. My ISP has installed a Fortigate FG-60E so I have hooked up the Decos directly to its ports. I assume this is what's causing the problem but have no idea...

I'm trying to connect my Decos X75 as access points all using the Ethernet backhaul. Decos are connected to the router and access point mode is on. But they are not connecting together via Ethernet,...