Hi @KitchenKnives 

The TV Engineers have responsed with an answer.  They say that the issue is with individual MKV files with certain conditions when it has been encoded.  Unfortunately the exact problem is rather cryptic and I cannot post it. 

However they have suggested the following solution/work-around:

Using a program called MKVToolNix : HERE - remux the specific MKV files.

Ive not used this program before, so....

My next question to them was : Will they issue a FW update to prevent certain 'error' files from totally crashing the TV - I await the answer.

Cheers