Having exactly the same issue with my MacBook Pro 13" (early 2015) that I bought new in November 2015. Took it to Apple, they say they can't replicate the problem therefore there is nothing wrong with it (which I'm pretty annoyed about) - I've discovered that if it does decide to switch off and become completely unresponsive, all I have to do is to physically turn it upside down, then back the right way up, and hey presto, it starts up every time.
...not sure I want to be stuck with a £2k mac that I have to keep fricking turning upside down though!