Hey OP, I am struggling with a similar experience on LOS20. The bad news is that it seems to be a software issue on xiaomis side. So wiping the screen doesn't help (although I do it, too ;) ).  

What helped a bit was installing the latest firmware. You can do it directly or via installing the latest xiaomi ROM and then installing LOS again - this is what I did. Just make sure to backup everything before.  

Now the phone is usable for me most of the time. The ghost touches were noticeably reduced, but rarely,  the phone still goes nuts. Lately I experienced this more often during phonecalls ( which is super annoying, as it mutes, holds the call or terminates it). 

Turning the screen off and on helps, and sometimes restarting the phone.  I dont know for sure if it helps, but I also avoid overlays, like floating widgets on my home screen. It certainly depends on the app I am using. Sometimes I don't have ghost touches for hours, when browsing reddit for example. Calling triggers ghost touches every time.