Found the problem. after connecting the archer c20 on another isp with a different modem everything worked great tested archer c20 in another house with my same isp and modem (an arris tg862a) , the...

@Kevin_Z thanks . my devices (mtk's and the c20) are ready when the enginneers mail me :)

@Ivaylo should i wait to @Kevin_Z answer or should i pm him?

as you can see in the video, the second android box connects, then disconects, and do that all the time until i set the c20 in router mode with client isolation

@Ivaylo yes, i have many other NON mtk devices, all of them connects normally non mtk devices that works normally motorola g8, sony ericcson android phone, samsung galaxy j5 prime, samsung galaxy...

Update: non mtk devices conects normally. Motog 8 plus : ok. Samsung j5 prime: ok. Samsung galaxy core2: ok. Mtk devices only one of them conects