Ok, Gintama fails quite hard. My Nvidia 960 can play it in hardware mode, on the S905 one gets a slideshow with sound. Here is a link to test:
Download File: [AnimeRG] Gintama - NCED_20 [720p] [x265] [pseudo].mkv - filecloud.io
Thanks for upload a short piece for testing. I can verify your findings with build 8.0.1l but playback has no problem with build 8.0.1l-mm. Therefore it's problem of the nougat kernel.
UPDATE: I also test the video on RPi2 and Odroid-C2. Playback on RPi2 (LibreELEC 8.0.1) failed as it did on S905 devices. However, playback was fine on Odroid-C2 with Raybuntu Krypton 12 build. Hope this additional information could help.