@TP-Link Thanks for the reply.

 

Just to clarify, I have the units set up to have the same IP address and password as the router.

 

1.When the 4220 disappeared from the APP, would the poweline light turn off as well? Or it would only disappear from the APP but did not affect its performance?

 

The lights on all units stay on.

I don't know if the units are still working or not, if I am picking up wifi from the TP units or only from the router.  Not sure I could tell? The reason I first noticed that the 4220 units disappeared from the app is because the wifi speed had reverted to being very slow and unreliable.

 

 

2.May I know the hardware and firmware version of the TL-WPA4220KIT?

 

I don't know. How would I know this?

 

The base unit connected to the router has the following on it:

Model: TL-PA4010(UK)   Ver: 3.0

 

One of the extender units has:

Model: 

TL-WPA4220(UK)    Ver: 4.0

 

I no longer have the packaging.

 

 

3. Are you always connected to 4220 when it kept disappearing?

 

See above, no idea if I am getting wifi from the 4220 units or the router at any time, other than sometimes the wifi signal is weak in some rooms and not at others.

 

 

4.Would 4220 come back after log-out and sign-in again or rebooting the 4220?

 

No. The 4220 units only reappeared when I reset the router as a result of trying to fix slow/missing wifi.