@Huge101 One more thing. Before you try upgrading M9 Plus firmware manually, power off Deco M5. So that your Deco mesh has only M9 Plus units online. Just in case.

@Huge101 That must be it. Firmware that old can't be updated through Deco app. Follow different, manual process: How to Update the Firmware of Deco

@Huge101 I double checked again, I have that option in my Deco M5. Just made screenshot and will put it at the bottom of my reply. I can only think of the following differences between your and my...

@Huge101 This feature is called "preferred signal source selection." It is documented here: How to select a preferred signal source on the Deco App My Deco mesh is two M9 Plus and two M5. I tested...

@mstarr3 It wouldn't be possible to tell if your powerline adapters are compatible with Deco mesh backhaul, until you try. For that reason, I recommend buying Deco hardware from the retailer with...

@Handpol The workaround is to find (borrow) WiFi router that allows channel change. Configure it to broadcast on channel 12. Place it near the Main Deco. Run Network Optimization on Main Deco - that...