Certain folks at the Kodi.tv forum have determined that a chmod to an internal system file could enable a cure, at least on a userdebug build where the system file is accessible. /sys/class/display/mode
When I strongly suggested this minor change be implemented by Xiaomi, the response was that it was an Amlogic problem.
Changing the permissions of the file is trivial but it causes a fail in the Google verification test.
This fault affects all S905X-H builds that are subject to Google certification.
If I was the bloke in charge of the Mi Box I would hire under contract some of the AMLogic LibreELEC Linux Kernel developers who actually know what they are doing.
AMLogic are not to blame here - it's the very poor amount of Xiaomi developer resources being dedicated to the AMLogic based Mi Box firmware that is the root cause of such issues. I do not know how much back and forth interaction there is with Google either. Seems very little. Xiaomi not setting display access mode permissions has nothing to do with AMLogic.
As an example the AMLogic box sellers WeTek and MINIX had this auto Framerate adjustment sorted out on their Marshmallow equipped AMLogic boxes over a year ago now, and then Kodi Krypton running on those devices has working auto frame rate switching.
There is however a bug in Google Android Firmware (display mode mismatch after auto refresh switching) that has to be worked around on AML devices to make this auto frame rate adjustment work correctly and not disable HDCP copy protection in the process which then results in non working Netflix. I strongly suspect this is why Xiaomi are very reluctant to implement such a feature.
MINIX with their AMLogic S912 U9 have this working 100% reliably.
Which is why I said interaction with Google themselves is important for a Google certified device.
OR
Have a Mi Box beta Firmware update escape with an unlocked bootloader and then let ROM developers like the Freaktab guys go to town on the Firmware and bug bust issues for free.