Stuttering Video on UHD (4K) files only

I’m not sure if this is an Android, Kodi, Nvidia Shield TV or Windows problem, but I am starting here.

Hardware / Software Chain…
HP ProLiant N54L running WHS2011
Drive Bender v2.4 hosting files (seagate 7200 drives)
Emby Server running on WHS2011 hosting Kodi library
Dell PowerConnect 2624 1Gb switch
Nvidia Shield TV 2017 (hardwired, all updates)
Kodi 17.1
HDMI cable to Vizio M60-D1 UHD HDR display.

Problem….
All SD and HD (1080p) files stream like butter over the local network. 2160p HDR files stutter only when the video gets very complex.
Example: Planet Earth II 2160p HDR (55min, 14GB, MKV) file streams fine until the locust scene where the entire display is filled with billions of locusts and the video becomes VERY complex. I don’t know how to explain this. It also started stuttering in episode 1 when there was a water scene with many ripples and splashes. I’m not sure if this is a network speed, buffering/cache, shield unable to handle, etc….

I’ve messed with advancedsettings.xml a bit.
buffermode = 1
readbufferfactor = 4
cachemembuffersize = 304857600 (300mb)

I think this may have ‘helped’ a bit, but it’s still stuttering. I feel like it recovers quicker with these settings.

Any help or suggestions are much appreciated.