So are you trying to flash a oem rom then? You shouldn't need TWRP unless your flashing a custom rom or rooting your device.
If so, I would try downloading one of the roms from here. You might be using a incomplete update rom when your flashing.
https://c.mi.com/us/miuidownload/detail?guide=2
Either use the MiFlash Tool, as mentioned on that page
or
Erase Data, etc.. in TWRP
Then flash it in Fast-boot mode using the included flash_all.bat from within cmd. Just make sure your using the correct rom for your device.