what build did you update to, ota or beta. if its the ota that's been around for the last month or so then yes it's buggy. Build 2179 is available on Reddit somewhere but you need to flash via recovery. Even with this the are still some reports of issues with some avr manufacturer's
Don’t know which update I have...it’s the official one pushed out. Now I have CEC enabled on both my LG TV and Mi Box, I am getting a “Mi Box now available” message instead...at least it doesn’t come up as often.
It says Version 8.0.0, Core version 4.9.54. This article says it’s Oreo. https://www.cnx-software.com/2018/06/26/xiaomi-mi-box-android-8-1-oreo-firmware/
The latest update a couple days ago solved the problem....
A factory reset after the update is highly recommended.