The Internet connection speed from Deco router dwindles down dramatically. My ISP provides about 500mbps. In the den, nest to the Comcast gateway, Deco generates same speed.  In one particular location 7-10 yards away, the Deco signal dies down to 6MBPS. Even if the Deco is  connected to the gateway via Ethernet cable, the Internet connection speed remains very inconsistent and very low in that part of the house - anywhere from 0.3mbps to 60mbps. At times the connection to the Internet would disappear altogether. And that despite the strong WiFi signal that my devices are registering, and Deco app reporting everything to be in good shape. In the same exact dead zone location,  the Internet speed generated by Comcast WiFi router remains very good - 300-400mbps. So, the problem is peculiar to the Deco. The second Deco located in the remote part of the house, about 14-20 yards from the main one, provides good connection speed - 200-250mgps. No dead zone there. This does not make much sense.

I upgraded the firmware. I swapped Deco units. I bought the third Deco unit. I changed the mode of the mesh network from Access Point to WiFi and back. I ran Network optimizatoin on Deco app. I enabled and then disabled Smart DHCP.  I killed the ISP WiFi thinking that it may have caused interference. I then enabled the "bridge mode" for the ISP router basically turning it into a simple pass-through modem. I tried different devices in the dead zone - 2 different iPads, iPhone, Windows 11 machine thinking that the problem may be in the network adapters. Nothing worked.

TP-link support is very difficult to obtain. There is no US support.  I have to communicate to a guy in Singapore. When he is on vacation, there is no one available at all. When he is in town and you need to talk to him, there is 12 hours time difference. His response to my emails is spotty and unreliable, I get his messages several days after having asked the question. Most importantly, he could not provide the answers. I have been battling this problem for good two months.

Does anyone have any ideas?