Hi Mattias, I believe more troubleshooting is needed in order get a chance to answer such question.
Perhaps you may want to try with a different Intel® HD Graphics driver: https://downloadcenter.intel.com/Detail_Desc.aspx?agr=Y&DwnldID=23886
Or updating BIOS (incrementally): Intel® NUC Boards and Kits — BIOS update instructions
Does the issue happen with different video formats (mkv, avi, mpeg)?
Are you connecting the display with any type of adapter/converter or a straight cable?
I have upgraded to the latest BIOS and the new beta graphics driver (10.18.10.3652), but that didn’t help.
I have only tested a couple of .MKV files with the same result.
The display is connected with a straight cable.
The GPU temp doesn’t get high so I don’t think it’s heavy loaded.
I connected a HDMI switch between the NUC and TV.
When the screen turns black, I can see at the HDMI switch that “connection led” blinks.
It’s as it lost it HDMI connection for a second.
When the screen was black, I started a remote desktop towards the NUC.
When I do that, the picture went back on the TV.
It seems that it has something to do with lost HDMI signal?
It looks that way but why it started working when you connected remotely? Was anything changed in the power settings?
Is it happening after 45-60 minutes each time you play the movie?
Can you test with a different display?