Just the chapter artwork screenshots, as generated in Subler, upon initial Metadata editing/tagging of the MP4/M4V. I then created the MKV with MKVtoolnix from that file, so it carried the metadata over.
I have these in all of my movies, though, and no problems with anything 1080p and less…
Unfortunately, it looks like the HW decoder on iOS/tvOS does not like this particular file, and this same issue can be seen in other apps that utilize the HW decoder. This is likely due to it being an 8-bit video with a BT.2020 color profile. To allow for HDR, the video really should be encoded in 10-bit.
Fortunately, as of 1.1, Handbrake does support 10-bit, but it will need to be selected manually after choosing the Apple TV 4K preset. See attached.
A quick test here shows that using Handbrake to re-encode the original Cliffhanger 4K source video into one using the Apple TV 4K preset (with 10-bit manually selected) does seem to work as expected in Infuse.