You should have no problems at all playing any 1080p MKV on Q10 Pro.
Even using Kodi native player you should have no problems.
The problems you describe sound like what you'd see if the box was overheating. Does the box get hot to the touch when playing the freezing files?
Otherwise, it sounds like you've tried what I'd suggest (last resort would be complete firmware reinstall). The problem could be hardware related, in which case contact your reseller for RMA.