I purchased a Mi Box 3 - Android TV to use on the HDMI source of my 4200NEX.  Actually, I've purchased 2 of them after the first one no longer worked while being connected to the 4200nex. 

Out of the box both Mi Box 3 devices connected through the HDMI source and worked fine.  They also both work connected to an LG TV and also work when connected to a Magnasonic Mini projector.

After the initial use with each Mi Box, turning the car off, changing sources, etc. caused no problems.   Leaving the device connected over night ended with both units showing no device for the HDMI source on the 4200.  Both Mi Box units work when connected to other devices and other HDMI devices work while connected to the 4200, including, iphone and apple TV. 

Does anyone have any suggestions?

I'm using a raspberry pi3 with Xbian installed, which is a flavor of Kodi.  I've found that the highest resolution the my 4200nex would allow is 576p.  You can see if you have that resolution available on your mibox, if not, a lower resolution like 480p works as well. 

Also, in kodi, there was a setting to allow video's to play at their native resolution, i had to turn that off so it sticks to the 576p resolution when i play a video.

If you even a little tech savvy, the Raspberry Pi is the way to go.

Anpass34

i have same problem with my Mi box 3 and a Mi Box 4 that all work on other connections. At first they worked in the 4200nex then they no longer work. I might have to down grade them to 576p

Did you ever find a solution that would allow the Mi box to work? Thanks. Selsomseen