@R1D2 OK. Thanks. I simply did not understand how it was supposed to work. I thought that changing the settings on the "master" (AP) would propagate to the Client. I have changed that now. I also changed to 40MHz fixed. Will test 20MHz again, this time changing both sides, but will do so after hours. I will also try changing to Auto.

I do have AES enabled:

@R1D2 It has been stable for several days, but today it acted up again. When it happens, the CPE210 closest to me stops responding to pings as well. This clearly indicates something else is amiss.System log on unit has no entries and it shows an uptime of several says so it does not seem to be rebooting.

@AndersG 

Hello,

exactly that action solved, as well, my conectivity problem. TPLINK should take a look into the topic and issue a firmware correction ... my network started to degradate after several hours (I even substitued one of my CPE210 by the latest V3.20); I tried everything that I could think about and no postive effect.

I was very close to drop TPLINK as a brand until I saw this hint! And it solved ...

But I see that the FW is still no solving it ...

Everytime it occurred I had to change something on the WiFi seetings and it would recover until ... some hours in the future. Quite anoying!

Here the latest:

So you can have an idea, this was the multiple effect:

I do think that TP-LINK must investigate what is going on. I am willing to send you all the config from the base AP, the client AP (ver 3.0) upgraded to the open-wrt OS (that unfortunatly doesn't exist, still for the version 3.2)

Thank you AndersG

To TP-LINK: should try to do it better, or please support other sw initiatives like openwrt ... to support your good HW.