Mi 8, the same problem. With Android 10 Magisk 19.3 and 20.1 ends in bootloops or "SU not installed". With Android 9 Magisk 20.1 not work, v19.3 do it.
What worked for me - after update to Android 10(the last OTA, ~10.12.2019), flash Magisk uninstaller then install Magisk 20.1 adding the 2 files...
Sometimes I think we have to wait for more L5 and E5a satellites. Also to take off the duty cycling (switch On and Off the GPS to save power). My Mi 8: MIUI 10.4 by xiaomi.eu 9.5.30 beta
I think the error comes from the apps using "google location services". View days ago a car assistance app located me 20km. away. Try to disable all the time google service in "Privacy - Location(here choose Device only, and under Scanning I have all in OFF) - Google Location Accuracy - Improve...
You better use another app, like HERE, my preferred free app. And disable "Google precision services" or something in GPS settings. My Mi 8 show me often 1 meter accuracy, most of the time - 2 meters, including cloudy sky.