I have Mi note 3 (jason), upgraded from stable 10.2.3 to stable 10.3.1, and the phone got fully wiped.
I lost everything in internal storage, but I did not perform a manual wipe.
Hope devs will fix this!
We've received similar reports in the past, and they are completely random. We flash ROMs almost daily and never encountered a sudden data wipe, so there's nothing we can do here.