@Optimus_Turf I made the solution myself by another simular post. Unplugging the 3 units and plugging them back in after a few minutes did the trick. Now I was able to add a device and all the...

I have a Deco E4-network that I set up 3-4 months ago and it works well. It was easy to set up and ad devices to (it has 3 units, all conected with ethernet backhaul). Now I wanted to ad "number 4"...