Mi two cents.
Mi5 pro, 128GB succesfully upgraded.
- Previously: BACKUP, BACKUP, BACKUP to MiCloud/whatever. I prefer to backup via TWRP and copy my backup to external storage.
- Copy new MIUI to internal storage.
- Update TWRP to 3.0.2.3 img from TWRP 3.0.2.2 via "install image" as recovery...