Chad Stewarthill it was grip for Nico at Hungary, but Mercedes said it was an overheated clutch for Lewis that was probably the cause due to the aborted start when Massa was out of place on the grid.
I thought they both had similar issues at Silverstone, not sure.
Regarding Austria, Lewis was managing an engine issue. Here is Paddy talking about it.
Regarding Austria:
"At the time, it looked like a mistake by Hamilton, but in fact it was anything but. He was slightly late in dropping his clutch but that was because he was managing a very tricky problem.
There was a fault with his engine, which was not responding to his foot on the throttle. It meant Hamilton had to guess the correct position to hold the throttle for the start, and hope for the best. Incredibly, he got it almost right.
Mercedes replicated the problem with Rosberg at the subsequent test and he could not get the car off the line without stalling, despite trying several times. Hamilton had in fact, Mercedes executive director (technical) Paddy Lowe said, done "an amazing job" to do the start he did."
Full article:
BBC Sport - British Grand Prix a win-win for Lewis Hamilton & Formula 1
But yes, they have to sort this clutch issue out, it's occurred too often and put them on the back foot. Not sure if going to manual will relieve or increase the issues........ But I'm personally glad more control is handed back to the drivers.