@Linder_B,

Does the Deco app show that the last node is connected to the network and is disconnected? You may still need to actually add the node to the network via the menu if it was not initially set up during the auto-setup window.

Providing a wired connection to your deco would definitely be the best way forward, as you can be sure that your other nodes will be able to connect to the node, and the ethernet connection will also provide a more stable method of communicating setup instructions or firmware updates.