Install Xiaomi Qualcomm drivers, then reconnect the phone in fastboot mode. Then use miflash if you want to go to official rom. Instead, download Xiaomi.eu rom and flash it with twrp.
sent from my Mi5
Lots of user reported that issue. So, you're not the only one. We should look at official forum (argh!) to see if it's a problem of the official ROM, too.
sent from my Mi5