@Alexandre. thanks for your reply! Your Office Deco is defective, you should replace it. There are no settings in Deco app to turn off/on Wi-Fi bands for backhaul. If you would like to, I can provide...

Hello! I bought 3 decos, and one of them (Office, in the image) is only connecting to the main deco (Living Room, in the image) using 2.4 Ghz, which slows down the whole network. They are close...