Have exactly the same problem as OP since a few weeks – but it doesn’t affect me that much because it happens on exiting the game anyway.
But I also have the crashes midgame like the other posters described since last update – mostly when I’m in champion fights with a lot of people. But it also happened in L.A. when I’m just walking around. And the last occurance was in a successful Marionette when I was walking to the big chest on the hill.
(so I had a successful Marionette after over 2 weeks and didn’t get my chest – thx alot Anet …)
Enclosed the crashlog – maybe someone from Anet have a look at it and give me some hints.