@NBW877 

Blue ziggy line means Ethernet connection. Have you by any chance connected new Deco M9 with Ethernet cable to your home network? If not, the culprit could be really old firmware version on your new Deco M9, reporting connection incorrectly. Updating firmware to latest version 1.5.6 should fix that.

I am not sure if firmware that old, 1.2.11 from 3 years ago (build dated 2019/09/26) can be updated through the Deco app. Check Update Deco in Deco app and if it tells you firmware is the latest, it just means firmware can't be updated through the app. Yes, I know, that is somewhat confusing.

In case Deco app won't update firmware, you will have to do it manually. Here is the process: How to Update the Firmware of Deco

I strongly recommend to update this new M9 Plus firmware to the latest. Doing it manually worth the effort. After it is upgraded to 1.5.6 manually, Deco app will be able to do firmware upgrades next time TP-Link releases new firmware version.

Also, it appears the clients in the garage (garage doors, lights) are still connecting to the kitchen Deco rather then the garage Deco. The kitchen Deco is about 12m away through multiple walls whereas the garage Devi is within 2m of all the WiFi clients in the garage. Very odd (to me anyway). 

  @Alexandre. 
 

No it is not connected via Ethernet. Only the main Kitchen Deconis connected by Ethernet. thank you. I will update manually as does not seem able to be done via app. 

 App reporting that all devices are using the old firmware, which they are not. Will manually update garage unit now. 

  @NBW877 

>Also, it appears the clients in the garage (garage doors, lights) are still connecting to the kitchen Deco rather then the garage Deco.

Devices that run on 2.4GHz only, such as older security cameras, garage doors and etc., are notoriously bad dealing with WiFi mesh. Their WiFi code may have been written very long time ago, before WiFi mesh was a common occurrence. That code might see Main Deco as a router and happily connects to it no matter distance and signal strength - because a normal house has just one standalone WiFi router, right? 

Having such devices with support for 5GHz means their WiFi code should have been updated reasonably recently to include WiFi5. This does not guarantee software developers added WiFi mesh logic into that code, but at least there is a chance they did. When buying new device such as security camera, "smart" something or anything else - look for WiFi5 support.

Also, I noticed at my house that sometimes it takes up to 24-48 hours for such devices to migrate to nearest Deco, so when you have everything on firmware 1.5.6 - just give it a day or two. I use smart plugs and when I bounce Satellite Deco M9 they are connected to, they reconnect all over the place and then gradually come back to closest Satellite Deco.

In case that does not work, and you have stationary clients in garage you want to have connected to Garage Deco but they don't, TP-Link offer beta firmware 1.6 for Deco M9 Plus, where you can configure how devices should connect. Not 100% guarantee they will, but at least you are in charge how they should - and if they ignore specific connection configuration, nothing else can be done other than eventually replacing them with newer devices.

The feature is described here, in Part 2: How to select a preferred signal source on the Deco App

Beta firmware is available here: Deco M9 Plus 1.6.0

Before you proceed with beta firmware you must have your new M9 Plus updated to 1.5.6 - and, as I said, just run your Deco mesh for 1-2 days and see if devices in garage migrated on their own to Garage Deco.

  Mall done. Thank you so much 

  @NBW877 

Now that everything is in order, you can bounce devices in garage (restart or turn their WiFi off/on) and see if some of them will just connect to Garage Deco. For those that won't, wait for 1-2 days to see if they'll need more time.

If after that garage devices still do not connect to Garage Deco, you now know how to manually upgrade your Deco mesh and can proceed with 1.6 beta firmware upgrade.

  @Alexandre. 
 

ha ha. Missed the 1-2 day bit. And I'm impatient. All good now though. They took about 15 mins to come back online but all good now. Thank you. 
 

I'm leaving wel alone now as all working and Al satellite units have strong signals. 
 

Thank you again 👍