Grey bars in HDR instead of black

Just some additional information…maybe can help…

I’ve tested 3 mkv files H265 HDR10 and here is:

  • how they work
  • video resolution
  • media info extracted with “MediaInfo for macOS”

Movie 1:
Full grey bars.
Resolution: 3840 x 1608
Media info: https://pastebin.com/raw/mK12wAHQ

Movie 2:
Black bars and on the border little grey bars with same height as the volume bar
Resolution: 3840 x 2026
Media info: https://pastebin.com/raw/npFuz98d

Movie 3:
Full Black bars (this is OK!!!)
Resolution: 3840 x 2160 (4K exact resolution!!!)
Media info: https://pastebin.com/raw/YHedMn3q

Any ideas?
I think that grey bars depend on the video height
And I think it’s not a PLEX bug. This bug is present on some versions of KODI, VLC, Youtube (screenshot on my previous posts) and other players.
Is it possible a workaround ? On KODI 18 (on my january 2018 beta) the bars are always full black.