[noggin]

I noticed that if I select all the resolutions in the whitelist so that the X900F does all the upscaling to 4K, I get jerky movement at times if MotionFlow is True Cinema (didn't test custom settings). Film mode can bet set to High without any issues. I wonder why that happens? The sources have been normal movies at 23.976 fps, resolutions ranging between 1280x536 - 1280x720.

With my set top cable box outputting the video as it is broadcast, there's no problem enabling True Cinema and Film mode High. 

I have a 49XF9005 (the UK version of the X900F I believe).   However I have MotionFlow entirely disabled - as I want to watch at native frame rate (or as near as possible) without any artefacts added by consume-grade frame rate conversion (I want to see the sources I play as close to the control room/grading suite quality as I can - and no control rooms or grading suites use MotionFlow-type processing).  

When you say 'jerky movement' what is the frame rate of the material you are playing and what is the frame rate you are outputting it at?  I can enable the MotionFlow on my TV and compare what I see with what you see? (I have an N2, a Minix U9-H, an nVidia Shield TV original version and an unhealthy number of Raspberry Pis and Chromeboxes)     

The source fps is 23.976. I don't know what the final rate is, I would expect the TV to use the 24p mode. But it doesn't show that in the display info, I see only 720p (looks like Kodi outputs at the closest fitting resolution if my source is like 1280x544). With no resolutions selected from the whitelist, everything works fine with MotionFlow at True Cinema.

I probably need to compare a 1280x544 and a 1280x720 source at 23.976 fps. Maybe the difference comes from what Kodi actually outputs.     

When you don't have Whitelisted resolutions selected do you still have Adjust Frame Rate enabled in Player settings (On Start Stop or On Start?)

What do things look like if you disable MotionFlow entirely?

AIUI True Cinema MotionFlow is for 23.976Hz content played at 59.94Hz content with 3:2 pulldown - it detects and removes the 3:2 to generate a 23.976Hz signal. This isn't needed if your Kodi source outputs 23.976Hz natively via whitelisting or adjust frame rate (as there is no 3:2 to detect and remove)?  It's really more useful for broadcast TV sources in North America (where 3:2 is standard for 23.976Hz stuff - whereas in Europe we don't use it)

I may be wrong - but that's my understanding of what True Cinema Motion Flow does.

(Sony used the standalone True Cinema branding for their TVs that accepted native 23.976p inputs back in the day. I had to replace my first gen 40" Sony LCD that did 50/59.94Hz-only with one that did 23.976/50/59.94Hz and was True Cinema branded - but without MotionFlow - when I bought my first Blu-ray player as I can't watch 3:2 - and no European TV uses it)