Hi! I had this exact same problem but I ruled out a hardware issue because every time there was slow to none response, if I turned the screen off and on again, it would fix it. I looked for a solution and after trying many, many things I discovered the problem was that I was using the Full Screen option offered by MI, i.e. the option to remove the three main buttons at the bottom of the screen (Back, Home and running apps) and to control the phone with gestures. After going back to the classic three button style, I restarted the phone just in case and I haven't had any more response issues in two days, I think it was a success!!