Sorry to hijack this thread, but I have a similar problem and my phone is not dead... yet.
I have a Mi4c bought at GB, which came with a shop rom version 8.2.1.0.0 and locked bootloader.
After many tries, I managed to unlock the bootloader unofficially, downgrading to 6.1.7 image through fastboot and unlocking also by fastboot.
Then I installed TWRP suggested in here: ...xiaomi.eu/community/threads/7-10-19.41961/ followed by the version 8.5 of Miui Eu ROM.
Everything went fine and I ended up with my phone on Miui 8.5.1.0.
But... when I tried to reboot to recovery, I found out I haven't got any!
I tried to reflash TWRP once again by fastboot but found out that I could't because Miui Eu 8.5 relocked my bootloader.
Tried to reflash official 6.1.7 again without sucess, even through EDL.
Now I can't install any official rom, either through update app, fastboot, Mi flash or Mi Suite and I can't unlock the bootlader officialy because I have an unofficial rom.
It's not that I don't like the rom.
The reason is I was having some sound issues that I thought it might be due to apps/files conflicts and I would like to try a clean flash (wiping system partition) and the in the previous instalation I didn't do a full wipe, and I still have the same issues.
Is there any solution for my problem or am I forever tied to this rom.