@TP-Link thanks for your reply. The issue happens only when interacting with the Echo by voice. All other integration with other devices in the LAN work perfectly when triggered from the app. It looks like the communication with Amazon's servers is cut off when talking to the Echo from what I hear in the recording accessible from my privacy dashboard on Amazon.

There is rarely an error message from the Echo but when one is returned, the error is just "I'm having troubles understanding you". I'm excluding problems with the device or on Amazon's side because I already tried factory resetting it.

I will try switching back to AP mode and report how it goes.

@TP-Link 

I discovered something very weird regarding this problem. The issue occurs only when the Echo device is connected via WiFi to the main Deco (the one that has access to the WAN). I tried moving it close the the secondary unit and it worked normally. Not only this, also when interacting with Alexa using my mobile phone I experience the same issue: when I'm connected to the secondary Deco it works normally while when I'm near the main Deco it says it has network issues.

In fact, I noticed that wifi devices behave better next to the secondary Deco than when they are close to the main Deco.

Is this a known issue?

@TP-Link 

Fast roaming was already disabled and Mesh was already disabled for the Echo. I tried disabling beamforming but the problem persisted. Other devices were having troubles browsing when connected to the main deco and the diagnostics tool was reporting a much slower internet speed for the main deco than for the secondary unit.

Switching back to AP mode immediately solved the problem.

After a while I reconfigured Deco to be in Router mode and surprisingly everything started working, even after re-enabling beamforming. The only change that I made was to use port 2 as WAN port instead of port 1 on the main Deco.

It took a while to get an internet connection because the main deco is connected to my ISP's router which is set to use bridge mode, so maybe that has something to do with it.

Anyway, I'll report back here if the situation appears to be solved or if it shows up again.

@TP-Link after a few days I can say the issue hasn't reappeared. Only once when I had to reboot my router and the main deco I faced the same problem but I could solve it by rebooting again.