@MediuM You should return this product. Deco E4 has 100Mbps Ethernet ports, which means it won't deliver faster than 100Mbps Internet connection speed. If you plan to buy different WiFi mesh set...

@Martijn43 In case you haven't tried it yet: yes, it will work. You can connect multiple Satellite Deco directly to Main Deco, if Main Deco has enough Ethernet ports.

@Sticko You should replace Ethernet cable between Satellite Deco and Main Deco. Based on your description, after Deco mesh reboot or restart Satellite Deco negotiates gigabit speed over Ethernet...

@Alpaslan Yes, this part is confusing with TP-Link Deco mesh: not only you must have correct Deco model, but it must be of correct hardware to support specific feature. From link I gave you, it must...

@HansJD Never mind me, then. It is common case for Deco mesh not to see device with static IP configured on it. Yours is not that case.

HansJD wrote @Alexandre. Good idea, but I run my total network on DHCP. @HansJD To clarify: do you run network on Main Deco DHCP service, or with separate DHCP server?