For clean flash you did wipe data also?
Thanks for your reply.
I just tried to flash again:
0) in Fastboot mode
1) fastboot flash recovery twrp-3.1.1-1-sagit.img
2) boot into the TWRP 3.1.1-1
2a) in TWRP, Wipe-> Advanced Wipe->Select EVERYTHING, then Wipe
2b) in TWRP, Wipe-> Format Data->type "yes" to confirm
2c) in TWRP, reboot to Recovery again
2d) boot to TWRP, connect to PC, copy the file xiaomi.eu_multi_MI6_7.7.7_v8-7.1.zip from the PC to the folder /SDCard in the Phone
3) in TWRP, flash xiaomi.eu_multi_MI6_7.7.7_v8-7.1.zip which is stored in /SDCARD without selecting zip signature verfication / reboot after installation
3a) after installation is done, Wipe cache/dalvik
4) Reboot System.
5) Hey it works this time!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
But one funny thing, if I boot again to Recovery Mode, it is the TWRP 3.1.1.0 instead of TWRP 3.1.1-1
I installed TWRP 3.1.1.0 before, but where's the TWRP 3.1.1-1 that I've just installed??