Update:
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?