Had you upgraded to the latest Plex Media Server prior to adding that mkv? If so, are subtitles still showing ok for films you added prior to updating PMS?
I ask because it sounds like you might be experiencing a potential bug I posted about here, where I’ve found that subtitles won’t display on AndroidTV for any new mkvs I’ve brought into Plex since updating PMS the other day. The subtitles for these films show ok for me on AppleTV and web player, just not AndroidTV.
