Bingo!
Xiaomi changes Mix2S model from "Global" to "China" via OTA update, which causes bootloop.
8.9.7 - downloaded OTA, rebooted -- now bootlooping to Recovery menu
http://en.miui.com/thread-3819702-1-1.html
My error message is "This MIUI version can't be installed on this device."
When I try "Reboot " -- it reboots right back into the Recovery menu.
. . .
I myself have a 8GB/256GB that was marked as an XA model. That model number became an "XE" model number after this OTA update.