[Boulder]

I set Smoothness to 2 (out of 5/Max) (plus Film mode/CineMotion to High) for the X1 Extreme based BRAVIA X900F and it is perfectly fine for me.

X1 Ultimate based BRAVIAs only have 3 notches for Smoothness IIRC. Dunno how Motionflow behaves there. 

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.