@SteveWex 

I just did in place upgrade of my M5/M9 Plus Deco mesh to set of X50-PoE. What I thought initially was incompatibility between M5/M9 and X50-PoE happened to be completely different issue: https://community.tp-link.com/en/home/forum/topic/710398?replyId=1463794

Can you share Deco model name(s) from X-series you use, and if they have 2.5Gigabit Ethernet ports - have you connected them to gigabit switch or gigabit port of ISP modem/router? Just collecting info here, thanks.

  @Alexandre. 

I'm using a mix of Deco:

3 x X55 (one of which is Main Deco)

2 x X60 (needed at the suggestion of TP-Link and no X55 available at my stockist)

1 x X50-Outdoor.

I originally had 3 x X55 and 3 x M5 plus the Outdoor node. Nothing but trouble and only just realising now it was because of the mix of M and X series. I know now because adding one M5 into the mix messed everything up again. Removing it and everything works again.

As for Backhaul, I had issues with this, but again, it could just have been the compatibility between the M and X series rather than the backhaul itself. I have not tried using Backhaul since removing the M5.

I still think its an app issue as when a node shows offline, the LED on the device is still green, hence my theory X and M series do not play well together in the app.

  @SteveWex 

Thanks. I have different X-series Decos: all X50-PoE hardware V2.

I can confirm I have experienced all issues you described, while doing in place replacement of M5/M9 with X50-PoE. Except Connection Preference loss, but about it later.

My plan for upgrade was to delete Satellite M5/M9 one by one, add X50-PoE in their place and replace Main Deco M9 Plus with X50-PoE at the last step. It did not go as seamlessly as I expected.

I may have had two issues on my hand: the one you described and the one which is specific to X50-PoE V2. If I knew what I'll face beforehand, it would have been easier for me just to delete my M5/M9 Deco mesh and start anew. I run Deco mesh in AP mode, not much to configure there.

Which means, I do confirm your warning and thanks for sharing your experience.

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Now that I went through the ordeal and my X50-PoE Deco mesh is stable, I am pleased with its performance. WiFi signal from X50-PoE is much stronger than with M5 and M9, which gets me better coverage. My M5/M9 WiFi mesh was four nodes, I now have three X50-PoE with excellent WiFi6 coverage everywhere.

There are also new features including IoT Network that I have not had with M9 Plus, and I needed it.

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In regard to Connection Preference in your Deco mesh. It will only be available if all Deco nodes support it. My guess would be, you have X60 which does not. If your X60 has hardware V1 or V2, its firmware will be 1.5.*. Connection Preference comes with firmware 1.6.

You can check X60 firmware version in Deco app.

If this is the case, you are also losing IoT Network feature, Reboot Schedule and some other features. Deleting X60 from your Deco mesh should bring them back if you need them.

  @Alexandre. 

I needed to add a node to my loft to be able to connect my home alarm system's base station to the internet. My house has foil backed insulation between the loft and the room below which has Main Deco, but just that one layer of foil scatters wifi so much. As I had M5, I thought I would add that in, but doing that started all the issues again, hence the post.

To get over it, I am now utilising a Powerline system.

Connection Preference is back now the M5 is taken offline, however the security is not. With X-Series only i had WPA3 option. Adding. M5 reduced it to WPA2. Since removing M5 I still only have WPA2 option.......

Beamforming also disappeared when adding M5 which was odd as Beamforming was available with my old system that comprised M5 and E4R. Beamforming was there with my current X55/X60/X50-Outdoor before adding M5 but not now.

I have no ECO Mode either. I think that's because TP-Link have no interest in X50-Outdoor any more, its still on 1.2.6 Firmware whereas X50 is at 1.6+ already. ECO Mode is useful, but only if available!

I hate Deco!