Upd: flashing stable version xiaomi.eu_multi_MI6_V9.5.3.0.OCACNFA_v9-8.0 without any wipes brings device back to life!
Upd2:
after successful de-bricking:
flashed 8.4.4 - all ok
flashed 8.4.12 - bootloop again...
MI6
Stuck on boot and finally reboots to TWPR
There are a lot of camera initialisation errors in log. Can't attach file - says it's to large (5.4mb) so dropbox link dropbox.com/s/x775zy371bcv5gl/andr-log.log?dl=0
Rollback to 8.4.4 doesn't help.