Qualcomm forgot to add this item in the source code of the driver, so that the phone works only on the channel width 20Mhz. It is Qualcomm's fault, but not Xiaomi.
Channel width setting allows you to control the bandwidth available for data transfer. However, wider channels are more susceptible to interference and can interfere with other devices. The 40 MHz canal is sometimes called a wide channel, and the channel is 20 MHz - a narrow canal.
Use the 20 MHz channels in the 2.4 GHz band. If 40 MHz channels are used in the 2.4 GHz band, problems can occur with performance and reliability, especially if there are other Wi-Fi networks and other devices operating in the 2.4 GHz band. Channels 40 MHz can also interfere with other devices using this range, such as Bluetooth devices, cordless phones and neighboring Wi-Fi networks. Routers that do not support 40 MHz channels in the 2.4 GHz range, 20 MHz channels are supported.
Post has been edited61rus61 - 10.03.18, 01:29