Why can MikroTik RB941-2nD-TC cut wifi speed to one of the network devices?

Question

WiFi

Guys, help needed! Available MikroTik RB941-2nD-TC (firmware 6.37.1 (stable)), desktop PC, acer laptop, two smartphones Xiaomi redmi note 3 pro (problematic) and Xiaomi mi4c. Provider "Corbina" 100 Mbps. The speed on the PC over the wire is close to the tariff one (around 90 Mbps). On a laptop via WiFi is the same. Smart Xiaomi mi4c over WiFi gives out around 70 Mbps. But Xiaomi redmi note 3 pro is no more than 15 Mbps. All devices in one room. At a familiar house, this Wifi smart gives out around 50 Mbps. I'm not smart enough to understand what could be the problem ... Thank you in advance for your help!

Answer 1

My redmi note 3 pro connects to mikrotik at 150mbps
so it's ok
use 5ghz

Answer 2

Export wifi config here. Most likely something with frequencies or channels or buffers.