@Kevin_Z  Do you consider the Deco P9 with AV1000 to be a Powerline Adapter? They do not appear to be able to connect to other Powerline devices by TP-Link.

Derek

@Breg90 I had the exact same setup. I actually read this post and I was encouraged by Kevin Z reply (https://community.tp-link.com/en/home/forum/topic/187492) before deciding to buy the  WPA4220.

I had the PA7020P v2 for the last 3 years running without any problems. 

I received the WPA4220v4, last week in order to expand the wifi, because due to COVID19 I have to work from home and the kids need also access to wifi in their rooms. 

I was able to pair with very little problems. It worked without a problem for a day or so, and then the problems started. 

Initially the PA7020P stopped pairing and the led for the powerline started glowing red or stopped being green. I tried pairing again, resetting to no avail. 

I tried removing the WPA 4220. That partially solved the problem. I.e. every 10 or 15 minutes I had failures in the powerline LAN. Again I tried pairing and resetting but the problem persisted. It is noteworthy that I had the PA7020P for 3 years without a single problem (I had almost forgotten about them).

In the end I  tried using an older devolo model that I had replaced 3 years prior (I wanted to see if I could get to 1000Mbps but I never got to that speed). After installing the devolo and everything is working. 

The way I've logged all this points to me, that either the devices are not compatible between them, and somehow introducing the WPA4220 made the (perfectly working until then ) PA7020Pv2 faulty.

I think this is something TP Link really needs to address if there are other occurrences similar to this. I've tried today to contact them in my country, and I will update this post depending on how this goes. 

UPDATE:  just under an hour after I sent the question the reply came in. It was short and brief. I was to send back to the retailer the devices that are under guarantee. The problem is that since the PA7020Pv2 were just out of warranty (I bought them August 2017 from a different retailer to the WPA4220). So now what I can hope for is to get back a single unit of WPA4220 which on its own is useless. I think the most economical and smart way forward for me is to cut my losses, and never buy TP link powerline adapter again.