@ClementA 

Hi,

It appears something must have gone wrong during the update of the Wi-Fi AP firmware of the TL-WPA4220. 

As per my knowledge, there is no official method available to recover from this. 
 

@woozle

Thanks a lot for getting back to me.

Using https://github.com/qca/open-plc-utils I can communicate with it:

plcstat -t -i eno1
P/L NET TEI ------ MAC ------ ------ BDA ------  TX  RX CHIPSET FIRMWARE
LOC CCO 003 xx:xx:xx:xx:xx:85 xx:xx:xx:xx:xx:54 n/a n/a QCA7420 MAC-QCA7420-1.5.0.26-02-20200114-CS
REM STA 005 xx:xx:xx:xx:xx:92 xx:xx:xx:xx:xx:5A 065 032 QCA7420 MAC-QCA7420-1.3.0.2134-00-20151212-CS

So I may be able to downgrad it and / or to re-do the upgrade, but I'm not sure it'll help much. What bothers me the most is that I cannot find how to access its web interface :-/

I've just tried

plctool -i eno1 -P /TL-PA4020P.pib -N firmware/FW-QCA7420-1.5.0.0026-02-CS-20200114.nvm -R xx:xx:xx:xx:xx:xx

and it worked successfully (the session finished with

eno1 E4:C3:2A:25:B2:85 Close Session
eno1 E4:C3:2A:25:B2:85 Reset Device
eno1 E4:C3:2A:25:B2:85 Resetting

... as expected I believe), but no change. Can I flash an older .bin using plctool? I can't figure this out.

  @ClementA 

The TL-WPA4220 consists of two devices built into one case. A Powerline adapter and a Wi-Fi access point.

What you did with the plctool is to re-load the firmware of the Powerline adapter, which, however, was working fine before. Hence it made no difference.

The firmware *.bin file from the TL-WPA4220(US)_V4_240220.zip is the firmware for the Wi-Fi AP. (the TL-WPA4220's web interface is part of the Wi-Fi AP)

  @woozle Thanks a lot for clarifying that for me. Are you aware of any method existing to re-upload the AP's firmware without being able to access its web-interface? Thanks!

I should also mention that I can see the device from the app, but it's not marked as serving as a WIFI AP, and "resetting" it does nothing, as far as I can tell.

  @ClementA 

Sorry, I've google'd myself and couldn't find any method (neither official nor inofficial) to recover from a broken Wi-Fi AP firmware on a TL-WPA4220.