I have deployed a Deco X55 system with 3 units, and generally things are working fine, however i've noticed some odd behavior with some 2.4Ghz devices, specially TP-Link KASA Smart Plugs HS100 for example which should be connected via the satellites, but the app shows the linked Deco as Living Room (Wired) which is the main Deco unit.

The two satellites are hard wired CAT6 back to the main unit, is the app just reporting oddly that the Main is the achor AP for these devices, and backhauling the traffic via the sattelite APs. most other clients show they are connected via (2.4Ghz) or (5Ghz) after the AP name, so the (Wired) is an odd one.