Your BOOTLOADER will be relocked after upgrade from Android 5.1 to Android 7.0 MI4C, Mi4S, MINote PRO so unlock it by en.miui.com/unlock after ROM installation again!!!
How to upgrade from Android 5.1 to Android 7.0 MI4C, Mi4S, MINote PRO:
Install MIUI 6.12.22 before updating to Android 7.0..
Select zip in Updater - menu - select zip
Unlock your bootloader again on Mi4C, Mi4S, MiNotePRO
(check your bootloader status by command "fastboot oem device-info")
Install TWRP for 7.0 via fastboot "fastboot flash recovery twrp.img" "fastboot boot twrp.img"
In case of issues, wipe /data in TWRP
For ROOT use latest SuperSU