I have seen this when the antenna is used for both Bluetooth and 2.4ghz wifi. I assume you are not connected to your router via 5ghz?

My honor 8x phone has the same issue. Caused by cheaping out on antennas or some other cost savings measure. If you google it you will see happens a lot with Chinese brands.

It would if:

Mibox supports 5ghz. I believe it does because I have the previous version and it does.

Your Mibox can be forced to use 5ghz either via your router settings (by using a unique ssid for 5ghz). Or by a setting on the box. Likely modern routers will allow you to set specific ssid for 5ghz.