First thanks for all your efforts porting LibreELEC to the Amlogic platform!
With the latest 8.2.3.1 I'm not able to watch a 4k movie (1080p is fine) anymore because after starting a 4k movie the whole screen gets split into two parts (up & down). In both screen parts the movie plays (but distorted) with some remaining part of the Libreelec gui as overlay. For me It looks like some kind of 3D mode although my TV is not capable of playing back 3D content.
With 8.2.2.3 everything was/is fine.
Like mule, I would like to give thanks for all the hard work!
I am also having this same (or very similar) problem. I needed to revert to 8.2.2.3 to get proper 4K rendering of either the Kodi UI or 4K video. I installed the previous version on a different SD card and the issues went away. When I try to switch the UI to 4K, the UI is painted to the screen twice, stacked horizontally (and thus distorted). When I try to play a 4K video, the view plays but the overlay appears atop, distorted (behind that, however, it does look like the video was rendering fine). I think this is the same issue as mule experienced.
I hope this is an easy fix. 