@sanderbaeten That explains it. You must have all Deco units in your mesh supporting "preferred signal selection." With the mix of those that do and don't, you'll be getting error message you...

@sanderbaeten I saw that error message for Deco mesh that has a mix of different Deco models. Do you have Deco other than M5 in your Deco mesh, for example M4?

@Exter_915 This is good configuration, as long as switches and modem/router support Deco Ethernet backhaul protocol. Check this document: General questions about Ethernet Backhaul feature on your Deco

@Dan1987 In Deco world, manual configuration of how Deco units should connect to each other is called signal source selection. That feature is described here: How to select a preferred signal source...

@Richardspain Please check what is the hardware version of your Deco M4. You should be able to configure how they connect to each other, if both M4 are hardware V4. The process to configure described...

@IanSutcliffe Have you considered the possibility that your master bedroom Deco unit may be defective, with broken internal antennas, and not properly broadcasting WiFi signal? I have Deco M5 at my...