I am facing the similar issue with my jio Airfiber which has wifi 6, when the wifi switch from 5 ghz to 2 ghz or vice versa, wifi speed reduced drastically, i have to either turn on airplane mode or restart my phone to get the speed, some when it comes from 5 ghz it is not connecting to 2 ghz automatically, i have to restart my phone to connect to 2 ghz, i am using nothing phone 2