Seems likely to me that the combined bitrate of all the video and audio tracks at that moment chokes the player out. I’d try remuxing it with just the video and one audio track (and any subtitle tracks you want) and then try the new MKV.

As far as your 24p situation goes - that’s odd, but you might be right in that it doesn’t like to do 24p output from a media file versus an authored disc. I don’t have the no-DNR 1080p, but the no-DNR 2160p and DNR 1080p both play fine and in 24p from my TV’s USB media player, and the DNR 1080p works fine on my KDLinks media player in 24p.