Black color turns to grey color after first playback

Hey guys.. I need your help..

This is my Setup:

LibreELEC 9.2.6 installed on an Intel NUC7i3BNK, which is connected via HDMI to a Samsung Q90R TV.

When KODI has booted and main menu is shown, everything looks brilliant, deep black color how expected.
As soon as I playback an offline video file (no matter if Full HD 8 Bit or 4K 10 Bit HDR Material) -> immediately deep black turnes into a grey tone.
Everything becomes lighter, and black becomes dark grey... disgusting

When I stop playing the file (even after just a few seconds), the menu looks differnt. I attached a before/after picture of my TV.
Just a reboot of the PC or a disconnect/reconnect of the HDMI switches back to original dark colors.

Additional hit: In System / Display settings I can enable/disable limited color range (16 -238),.. no matter whether it is enabled or disabled, the problem persists:

- limited range disabled (0-255): black becomes dark grey
- limited range enabled (16-238): dark grey becomes lighter grey.

I created some detailed debug logs:

- Playback and Stop of an mp4 in h264 with 8 Bit and 1080p
- Playback and Stop of an mkv with HEVC, 10 Bit HDR and 4K
- HDMI Reconnect, which resolves the problem

Any ideas?

Oh my god thank you!! That was the problem, it was set to Auto and obviously, Samsung has problems with "automatic detection".

I set it now fixed to low, and now it looks always the same.

You made my day smp!