Intel NUC white screen & VLC media player

I have an Intel NUC7i5BNH powering a 4k video wall. On boot, I have a startup command launching VLC media player and play a video on loop in full-screen.

This works fine, but after a period of time (anywhere from an hour to 4 hours), the screen goes white and the PC is unresponsive to keyboard or mouse input (except Alt F4), but when I single-press the power button, it pops up the 'Power Off, Restart' etc option box and I see VLC playing the video in the background. I can then cancel that and continue playing, but this is not workable obviously as this video wall will be unattended.

It looks like a hibernation issue, but I've gone through all the Power settings I can find. I've tried Ubuntu 16.04, 18.04 and 20. I've also updated to the latest BIOS. I've tried disabling hardware acceleration in VLC.

Any help or advice would be appreciated!

Thanks.