@Golfetta Different M4 hardware versions is the problem. TP-Link only has M4 V4 firmware that allows to configure how Deco connect to each other. When you added M4 V2 to your mesh, not only they do...

@gareth820 ... and one more thing: if you reconfigure your Deco mesh in Access Point mode, you'll have options on how to more evenly distribute clients between Deco nodes. I can discuss these options...

@gareth820 You have invested a lot into Deco mesh system, it would be waste if you just replace it. Also, with the new WiFi mesh you may have same issue. I have suggestions for you to try, perhaps...

Aidy2020 wrote @Alexandre. Thanks again, I tried this but I have quite a few products that don't work on 5GHz. Specifically Nest doorbell and smoke detectors and a few other things so that...

@Aidy2020 The only other thing left I could recommend is to configure Deco mesh to run in Access Point mode and test speed again. How to set up Deco to work in Access Point mode This is how I run my...

@Aidy2020 I have Deco M9 Plus. It is capable of delivering peak WiFi speeds of 650Mbps and steady WiFi speeds of about 400Mbps. For 500Mbps Internet link Deco M9 Plus is the right hardware. What you...