Needed to perform "format data" in TWRP. Afterwards the ROM installation worked properly.
Battery life is as good as on miui9 on my mi6. Did not face any battery drain in the last week since I installed 8.6.21 v2.
Last update to 8.6.28 could be "dirty" installed without any issues.
There are still problems with the notification on the lockscreen (some apps cannot be set to "show on lockscreen") but that's the only issue I faced for the moment.
Gesendet von meinem MI 6 mit Tapatalk