Letterbox bars going grey on Dolby Vision UHD

[bendermac]

I've watched The Hunt for Red October on 4K UHD with Dolby Vision and in a couple of scene the black bars turned kinda greyish. They were really noisy. A similar thing was with the movie Skyscraper. Is this a problem with the Dolby Vision layer?

If someone with the movie wants to check, jump to time 2:02:30, underwater shot of the passing by sub.

Playback with a Oppo UDP 203 on LG OLED C7 - Both Devices are on the current firmware.

UPDATE 1

Geoff told me on how to disable Dolby Vision with the Oppo and after testing it, I can confirm that this is a problem with the Dolby Vision layer. When the movie is played in HDR10 the black bars stay solid black.

UPDATE 2

After I've changed Dolby Vision Processing from Player-led to TV-led, the black bars are now solid black