I have OSMC on a Raspberry Pi.
When I want to play a specific mkv file, the unhappy smiley is displayed and then it comes back to the home screen.
To help you diagnose the incident, the mediainfo file is there: http://paste.osmc.io/haqaweseka.tex
And all the log files are pasted here: (I activated the debugging mode and rebooted before by following the instructions on the wiki) http://paste.osmc.tv/jehoronafa
HVEC/H265 need to be decoded by the CPU (as the GPU on the Pi doesn’t have such decoder) and the CPU of the Pi1 is just not powerful enough for the job