Same problem here, too.
Downgrading from developer 8.8.16 to any developer with Android 7.1 failed. Bootloop.
Flashing 8.8.16 again, no problems, but ugly camera.
Tested with serious twrp, deleting dalvik/wipe cache and data, but no chance.
Hello, excuse me for my bad English. I had such a problem. My phone became a brick after Downgrade! I recommend this to happen:
1. Installing stock Global Stable 184.108.40.206 with XiaoMiFlash with clear all, but without locking the bootlader!!!
2. Installing TWRP 220.127.116.11 for Xiaomi Mi Note 3.
3. And now instaliling xiaomi.eu global stable 9.5.8 .
4. Optionally instaling Root and more!
5. Good luck!
6. I drink beer!