Make a full backup to PC and check it. I have to erase data even with change Miui (android 9) to AOSP (android 9). Upgrade 8 -> 9 should be ok, but reverting 9 -> 8 = format data.
0. Make a backup to PC of all needed data from phone.
1. Flash TWRP from 9.8.1 thread, it should be something like 3.3.1.34 version
2. Format data in TWRP in Wipe menu (you will lose ALL data on your phone). You need exactly to Format data (gray button at the bottom), not just wipe.
3. Copy...
I can only handle this:
1. Flash TWRP 3.3.1.34
2. Format Data (lost all data include internal storage)
3. Flash 9.8.1 (Pie)
4. Restore google backup
5. Dirty flash 9.8.22
AlarmManager round the time of *_WAKEUP PendingIntents by 5 minuties. For Example, if PendingIntent triggering time should be in 2 minutes it will be in 5 minutes, 6 minutes extends to 10 minutes. This bug make all timer and alarm apps broken.
Downloaded themes from market works good, even if theme is not empty :) A have my own icons theme, do you know how to add it into theme market (for free, of course)?
After 2.9.21 I have a strange issue with incomming calls. For example, if somebody with number +7911911111 calls me it shows like 9119111111 (without +7). The bug is not persist on every unknown phone, just in some cases.
Galaxy Nexus GSM
Sorry for my English :)