Update, I tried again and a fresh install onto SD card and still the same locks up when stopping a video file...
But I installed -
LibreELEC-S8X2.arm-8.2-MXIII-PLUS.img.gz
And so far its working great oh just one thing Im guessing thats for the 2gb version of the box?
Do you think it's a problem with Kodi 18 being incompatible with the s812 box?
Thanks