@David-TP 

Let me explain it a little bit more. And wheter or not the power adapter is connected firmly (really??)

Every unit is on a seperate floor and all power units are connected firmly. What I have noticed is that Wireless devices, out of nowhere, just lose their Wifi Connection. They is no connection with the default wifi network anymore on the iphones, ipads etc. When I go to the main unit, I don't see any LED's on or flashing which indicates (to me at least) it is not rebooting but I am not sure. The setting in the app is LED = OFF.

I have not tested yet what happens with Ethernet connected devices but that Wifi is suddenly lost completely is weird of course.

After my initial post I have disabled Beamforcing too (after already had MIMO and Fastroaming to OFF) to see whether this helps.

  @M0untainD3w

sounds a little familiar what i am currently experiecing.

https://community.tp-link.com/en/home/forum/topic/644014

  @David-TP 

OMG....this is getting really frustrating....

It just happened again. I am not home at the moment but I got a notification that a device lost its VPN connection and now does not want to reconnect.

My camera's, running through homebridge, lost their connection entirely and needed a reboot to rejoin the network. READ: I cannot reach them anymore after the Wifi completely shutdown.

This is really unacceptable for a product I paid over €330 for!

  @David-TP 

Hi David,

I also called the local TP-Link Office who couldn't help me either, other than the fact they mentioned one thing that they were quit firm about, which is that I had spaces in my SSID. So my SSID#1 was something like: My Wifi Network. So i have changed that in one name: MyWifiNetwork. Also I enabled the LED again.

Regarding your points:

1. Set the main Deco to 5GHz only with SSID#1

A: I couldn't set it only to 2,4ghz as I have some devices that won't work anymore. And we don't know when it crashes, we won't know how long to run it like that. So if there's absolutely no other way, I need to change it. As it stands now, I have SSID#1 set to 2,4ghz/5ghz and with one name: MyWifiNetwork (no spaces)

2. Enable IOT network for 2.4GHz only with SSID#1 and connect the smart home devices to the IOT network.

A: That was already the case and I haven't changed that. The difficult thing is that I am unable to test whether everything keeps on working as my main laptop loses the connection. What I did found out that specifying a dedicated DECO for IOT does not work. Having a smart home device connecting to the IOT network on 2,4ghz, it just randomly chooses a DECO (even if i specifiy). If I switch to the main network SSID#1, it works fine and connects to the DECO of my choice. Not sure if this helps.

3. If you don't have any 6GHz compatible devices, please set 6Ghz to dedicated backhaul only. You could check whether whether both 2.4GHz and 5GHz had the same issue.

A: That was not the case first but I have changed that too.

FYI: It just happened 30 mins ago and from what I can tell, devices lose their connection to the mainnetwork, SSID#1. Ethernet enabled devices (to the main DECO) stay connected and the LED stays Green. No flashing, no other color.

FYI2: I have saved the logs on two occassions (from the web ui) when it happens. Not sure if it will help and if there's no specific sensitive data in it, I can share that with you. Not through this forum but in another secure way.

  @M0untainD3w 

In addition, i have now completely disabled the IOT network and used that SSID (and 2,4 GHZ only) for the Guest Network to see what happens.

  @M0untainD3w 

And it just happened again.....for crying out loud. Normally every seems to be getting back in place in a couple of minutes but now I needed to reboot the main unit. What was strange (this time then) is that I seem to be able to find my SSID's still, the Main and the Guest Network, which leds me to believe the 2nd and 3rd were still broadcasting.

On one moment I was able to connect but did not get an IP from DHCP, which makes sense if the main unit was failing. And after rebooting that (powering off completely) it was working again. The local TP-Link people also suggested to switch Deco's. I will try that tomorrow.

But to be honest, this makes me very very sad......Especially because I got rid of the boxes and I have no idea what to do when this stays this way.....

  @M0untainD3w 

Ok, i am completely done with this!!

Yesterday, I had an epiphany or at least I thought I had. Every time I changed routers (in the last 15 years) I always choose my own subnet. So what came to mind was that maybe this TP-Link software gets messed up (routing tables etc) on the guest network and it hangs then. 

So I have done another factory reset on all three nodes and switched the main one with another (suggestion from local TP-Link) and left everything default on the DHCP server part, the subnet.

And today, AGAIN!!!! Total unresponsiveness inside the house but some DHCP clients with a reservation (doorbell) were reachable from outside. The wired devices still had a conntection (internet works) but my phone, that just got home could not connect. My laptop the same.

I am done with this. I am not paying €330 just to troubleshoot for 3 weeks to get a simple wifi connection. So now what @TP-Link??