[fritsch]

Nobody knows ... post your damn Debug Log.

Here you go... http://xbmclogs.com/pthzwxo9d

Incidentally, while disabling refresh rate syncing with the video, I played with several combination of settings:

I tried...
1. Kodi Limited, GPU Full, TV Limited > required black level of 50, WTW/BTB preserved
2. Kodi Full, GPU Full, TV Full > required black level of 50, WTW/BTB clipped
3. Kodi Limited, GPU Full, TV Full > required black level of 35, WTW/BTB preserved
4. Kodi Limited, GPU Limited, TV Limited > required black level of 35, WTW/BTB preserved
5. Kodi Limited, GPU Limited, TV Full > required black level of 25, WTW and BTB preserved

Observations...

A. Every combination has some subtle but noticeable lines through the grey ramp. Their frequency spacing seemed to change with each scenario but they never completely disappear None of them are as smooth as my Mac.
B. I have been leaving my contrast on Max as it hasn't impacted WTW until tonight when it was too high for the full range of WTW on scenario #1. I had to reduce contrast to 95 from 100 (Max) in order to see the full range of white tones above 235... is that a good sign?
C. I assume scenarios 3-4 that required a lower black level means there was an unwanted conversion in levels occurring? Why the lower black level?
D. What's going on in scenario 5 that requires an even lower black level?

Can anyone else comment on what's happening as black levels need to be reduced from 3 through 5?
Why are 1 and 2 the same black level? Isn't Kodi converting levels in 2?

Concerning your Adjust Refreshrate to match video bug - there is nothing in the log - it switches happily to 1080p24 in your log.

4. Kodi Limited, GPU Limited, TV Limited > required black level of 35, WTW/BTB preserved
5. Kodi Limited, GPU Limited, TV Full > required black level of 25, WTW and BTB preserved

That absolutely makes no sense ... as the GPU will scale twice ...

1. Kodi Limited, GPU Full, TV Limited > required black level of 50, WTW/BTB preserved

Good setting

2. Kodi Full, GPU Full, TV Full > required black level of 50, WTW/BTB clipped

Everything is scaled to full range 0 .. 255 with dithering on top.

3. Kodi Limited, GPU Full, TV Full > required black level of 35, WTW/BTB preserved

This does not make any sense at all either. As we will output colors only within 16 to 235, while your TV expects: 0 .. 255, so you will have neither black (will be gray) nor white (will be light gray) ... You also cannot adjust it correctly with the brightness (it's additive only), a contrast spread would help, but that setting is also fully wrong ...