This sounds more worrying now. When I heard it originally it sounded like a mountain wave. Those are extremely powerful natural downdrafts (or up!) and common in South New Zealand.. They've crashed flights before: https://en.m.wikipedia.org/wiki/BOAC_Flight_911 though that was at mount Fuji in Japan.
But if the plane did this by itself.. wow. The 787 is fly by wire. Worrying. And very bad timing for Boeing.
But if the plane did this by itself.. wow. The 787 is fly by wire. Worrying. And very bad timing for Boeing.