Thanks for all your replies. To address a couple of them, I used a popular bike specific lube on the chain manufactured by WD40 - no deep cleans or anything out of the ordinary. The chain felt like it was meshing fine.. as I type this I'm wondering could there be a mis-match between the chain wheel and the chain? If the chain wheel is steel and the chain links are softer stainless, and the teeth of the chain wheel are fractionally too far apart for the chain...?
t's just a thought. I really don't know but I'd rather not just accept it as a freak occurence. If I just stick a new KMC Z9 chain on there I'm basically saying that I put the failure down to a rouge chain - but why so many links over so few miles?
No answer back from vendor or KMC as yet but I'll post on here if I hear anything. Thanks again for your input.