[S905X3] X96Air_P2/P3 4/32GB 1Gbit Lan (How to config)

So yesterday I have successfully installed the current stable version of CE on my new X96 Air P3 4/64GB. Everything seems to be fine, except the following:

I have downloaded the Big Buck Bunny short film from the Blender Foundation YoutTube channel to test 4K@30Hz and 4K@60Hz:

The 4K@30Hz version works as expected, but the 4K@60Hz is stuttering badly, clearly visible from the vertical pan within the first 15 seconds of that video. Both version use the h264 codec.

The equipment should be well capable of 4K@60Hz, so what am I missing here?