@oller I'm having the same issues

Just sent an email to TP Link support, I'll copy paste it here since my experience might be useful to the community

The firmware of my unit is up to date, on version 1.5.1

The ping issue is present also when connecting my laptop via ethernet to the main deco, but it’s not there when connecting my laptop directly to my modem, so the issue is in the Deco.

The issue started from some weeks ago, when i updated the Deco from 1.5.0 to 1.5.1, the issue might be the update, but I’m not certain about it

The network map is in the following image. I can make some clarifications regarding it:

The main deco (called “estensione”) is connected to the “Sala Giochi” one wirelessly, most devices are then connected to the Sala Giochi one either trough Ethernet (there is a switch) or wirelessly.

The “Camera di Ale” is connected via ethernet backhaul to the “Sala giochi”.

The “Serra” is connected wirelessly to the main deco, but the thing that I find really strange (in the past it wasn’t like so) is that the “Study” Deco (that is an M5) is not connected to “Serra” that is the nearest one, but it’s connected to “Estensione”. In the past it wasn’t like this, “study” was connected to “serra”.

Here is also a screenshot of the ping spike test, ping spikes are variable, not Always like this, but still WTF

PLEASE FIX THIS ASAP it’s not acceptable to have such issues

I think I found to problem about ping spikes . when I close the (Mesh Technology) the ping spikes problem will be solved . 

@fl00000 @TP-Link can you please transfer my case to the senior engineers? I tried your solution but with it my computer still have some connection/ping issues with the network...   

@Jzlim Hi, how have you gotten on with this issue? I am currently facing the exact same issue with the M4's.

@TP-Link I have bought two Deco M9 Plus units recently. I have seen the same problem while gaming and can confirm that disabling mesh technology, fast roaming and beam forming has helped. Disabling the technology that gives these devices their leverage leaves a bitter aftertaste though. 

@oller 

Just intalled it all and had propper teliporting ping straight away. Changed the m9 to access point mode and sorted. (had to reboot plusnet box.

suspect it was a conflict of two routers. will try turning off plusnet router at some point so I have the tplink controlls on everything.

The only fix I found to the ping/lag spike issue (going from 4-10ms up to 2000ms every 10 seconds) on my Deco M9 Plus was to:

1. Split the 2.4GHz and 5GHz on two seperate SSIDs.
2. Disable mesh technology on devices that have issues (Example: Asus USB-AC53 Nano which uses a Realtek chip does not work when enabled).

To split the frequencies, launch the Deco app and do the following:
1. Click on More > Router Settings > Wifi.

2. On the Main Network, disable the 2.4GHz frequency.

3. Enable the Guest Network, disable 5GHz, disable Isolated From Main Network and set the security to AES or AES+TKIP.

4. Ensure the SSID is not identical to the main network.

It has been working great since (IPTV, Multiple Meet & Team meetings, GeforceNow streamed gaming).