It's too easy to write this off to 'bad luck'. That's just a way of admitting Mercedes don't understand what's going on. There is an underlying cause and actually I don't believe that Mercedes don't understand what it is which makes me think it's something they don't want to admit. Is it an issue in the way Lewis drives his car? Possibly although even if that were true it's not like Mercedes wouldn't know that after several years and design their egnine accordingly. Also even if Lewis is more agressive on the throttle or what ever, it doesn't explain why a brand new ICE blows up in less than one race weekend? In any case if it is the driver would the team want to publically admit it? Probably not, but then again I'm sure they'd make the driver aware and not expect him to go spouting off about it to the media, so I think we can assume it's not that.
Hypothetically, might Mecedes favour one of it's drivers over the other? Might it suit Mercedes, the German brand, to have a German champion? When the team has the luxury of being so far ahead of everyone else that winning both championships is beyond reasonable doubt even at the start of season then I do not believe a conversation wouldn't be had about who they would prefer to win. If you accept that situation, it's not much of a leap to wonder how that possibly might effect the season?
The counter argument is how does a German parent company persuade the children companies based in England and employing largely English people to favour the German driver secretely and not expect someone to leak that information? As reasonable a CT as it might seem, the actual execution is nigh-on impossible.
What ever the reason, and I doubt we'll ever know, it's looking more and more likely that LH is going to lose this DC due to unreliability. How he responds to that will be interesting. With the regulation changes coming in next season, if Mercedes dominance is broken and someone else becomes the top dog I would expect Lewis to move teams in 2018. I don't think he's the forgive and forget type.