Whatever it was it must have been patched a long time ago as I haven’t encountered it in a long, long time. I just remember it alongside the troubles I had getting everything working properly due to not knowing enough about hdr, new kodi box, first 4k tv (lg). I spent hours ssh into the shell querying the hdmi output on various kodi and tv settings and playing various videos. Every time I got a blank screen followed by a no signal message my heart sank a bit more.
All I remember is I finally figured out how to reliably enable switching to 4k24 4:4:4 hdmi link for hdr films and it’s been great ever since.