@EnginWiFi 

Hi, Have you tested the Ethernet speed from the main Deco?

And how about the link speed on the phone or laptop when they are connected to 5ghz of the main Deco?

https://www.tp-link.com/support/faq/2265/

At the same time, please check the QoS settings on the Deco APP:

Deco APP>>>QoS>>>(Set Application priority to Standard, Remove all high priority devices, set the Bandwidth to 1000Mbps upload and 1000Mbps download)

Thank you.

@EnginWiFi 

Hi,

So currently, the Ethernet speed from the modem is 287/286 m/s; Ethernet from the main Deco is 237/285 m/s, 5G from the main Deco is 197/243 m/s(link speed is 866.7m/s), right?

For the Deco X60, the maximum link speed is up to 2402m/s for ax standard with MU-MIMO supported, while the test device is 866.7m/s which is only ac standard.

So 197 m/s out of 237m/s  on 5ghz, the speed is quite acceptable for the tested devices.

And The cable in the box is capable of 1 G/s.

While, if once the satellite Deco was connected to the main Deco via cable, the Wi-Fi speed drooped to 70-90m/s again, which is not normal.

And it seemed like the device automatically picked up the 2.4ghz first, instead of the 5ghz.