SOLVED: TROUBLE PLAYING 4K CONTENT

[TheDreadPirate]

You're software transcoding and not fast enough.

Stream #0:0 -> #0:0 (hevc (native) -> h264 (libx264))
...
frame= 193 fps=2.7 q=28.0 size=N/A time=00:00:08.00 bitrate=N/A dup=1 drop=0 speed=0.11x

I see you are running Windows, but what are the rest of your hardware specs? Do you have hardware accelerated transcoding enabled? And what model iPad? The ffmpeg log you included is for a 10 bit HEVC video. 10 bit HEVC decoding was added in the Apple A9 chip that came in the 2017 iPad.