@Mat2c I have 14 devices between 2'4 and 5 ghz, so I don't think this is the cause. And with 1.2.x was ok.

@Mare007 Look at blocked devices (I think it is under firewall). Some times C6 blocks devices it thinks are dangerous (many intermitent connections, for example). The device seems contacted, but...

@Wetterhahn No, the problem appeared in 1.3.x. Prior firmwares were ok. I have been using this router intensively 5 months before the 1.3.x distaster.

@Kubas Yes, but with openwrt in the middle, because tplink has prevented going from 1.3.x to 1.2.x. Or perhaps it is possible to go fron 1.3 to 1.2 with tftp (I didn't try). With the web interface it...

@Kubas I followed this procedure from ofiicial to wrt and from wrt to official: https://openwrt.org/toh/tp-link/tp-link_archer_c6_v2

@RedIndianRobin From 1.2.x I have installed openwrt and then gone back to 1.2.x using tftp. You just follow openwrt instructions. But in wrt 5ghz is not stable enough yet.