@GeorgeSA Hi, Please turn off the 2.4ghz on the Deco E4 and leave the 5ghz only; Then disconnect or forget the Wi-Fi network again to have a look; By the way, Did all the 4 Deco E4 connect via...

@Idan99 Hi, since all the Deco units under the same Mesh would be under the same operation mode, did you want to set up main Deco under wireless router mode and 2nd and 3rd Deco under access point...

@irfanjamal Hi, would it be possible to provide a picture of the floor map about the location and distance of each Deco? Have you tried to reset the whole Mesh system before?

@Kupsul Hi, is your ISP modem a pure cable modem or modem-router combo? If it is a router, it is ok to connect two E4 units together; And it is also suggested that you could switch the operating mode...

@Auror1968 Thanks for the update. It is not supported yet and May I know the reason for the request? And I will keep attention to the similar feedback for further evaluation;

@Oxford Thanks for the update. Have you tried to change the DNS server, like 8.8.8.8/8.8.4.4 on the Deco APP to have a look as well: https://www.tp-link.com/support/faq/1855/